Simply put, the answer is because of the influence of West African music on "Western" musical traditions.
If western Europe is the mother of harmony, west Africa is the mother of rhythm. Is that a trite oversimplification? Of course, but it's a meaningful start.
By analogy, it's fair to say that with the introduction of European music to much of the world, the entire harmonic language of the popular music of those countries changed: complex harmony involving cadences, modulations, even the very idea of "chord progressions" is something that isn't found in much of the indigenous music of much of the world, which is often either modal, strongly melodic, or drone based. When you hear bollywood music that involves an "indian sounding" (i.e. microtonal) melody over a band that nevertheless changes chords, that is down to "western" influence on Indian music.
This is a story that is universal to music worldwide, musical traditions both modern and ancient are inevitably products of other varied music traditions that a people or culture have contact with. The history of "western classical music" (or common practice period music if you prefer that term) is full of
influence from the different and varied folk traditions of different peoples within Europe.
The concept of multiple overlapping semi-regular rhythms that all exist relative to one inflexible metronomic pulse, and interplay with each other to collectively create a "groove" is something fundamental to West African music, and something that is largely absent from Western European Common Practice Period music.
In a lot Western European art music, the pulse of the music is something that ebbs and flows, and pushing and pulling at the rhythm is part of the musical expression (much as is true dynamics, areas of light and shade create deeper expression). In music like this, the use of untuned percussion to "keep the beat" is something that stifles musical expression rather than aids it, and so for orchestral music (except in some more modern works) untuned percussion, even when present in large numbers, isn't there for the same purpose as untuned percussion in modern popular music, it's there to give colour, to emphasise certain sections and certain moments, it's there to build tension and give release, but it's rarely used to "keep the beat" as with African drumming, jazz, pop, or EDM for example.
This flexible expressive relationship to rhythm is something found across European art music throughout the common practice period, and contrary to some popular belief is not a "romantic invention". (In fact, applying strict, computer-like approach to rhythmic interpretation when playing say bach is very much a modern invention, but this is another conversation).
There is of course European music in which the pulse is less flexible: dance music like jigs necessarily has a more regular pulse, and even more so with music for marching (military bands which obviously also influenced popular music, it's where the snare drum comes from after all). But even in these dances and marches, there is once, constant rhythm being played throughout the music, by one drum, or multiple drums in unison, you don't find the "groove" of West African music (multiple overlapping rhythms).
Modern genres featuring prominent use of untuned percussion such as jazz, rock, pop, funk and most electronic music follows in the footsteps of west African drumming. The expressive possibilities of a pulse that ebbs and flows (Chopin's music for example maximises this) are abandoned, in favour of a different set of expressive possibilities that come from a fixed pulse with multiple interweaving rhythms. In Latin American music and west african music, this is mostly achieved by multiple drummers playing together, each one on a single instrument (a Samba rhythm section exemplifies this).
In jazz and rock for example, the drum kit essentially performs the role of allowing one drummer to perform the role of multiple instruments simultaneously, while additionally giving that drummer more creative control to change the beat as and how they please (leading to the "fill", something much easier to achieve with a kit than a group of musicians). Listen to the drumming on "superstition" and it's possible to imagine 3 dudes playing separately on a hi hat, kick drum and snare drum, who all occasionally stop for a second to allow a fourth dude to smack out a fill on another snare drum.
This ability to play distinct independent parts simultaneously all while creating a global groove is one of the most impressive things (to me at least) of "drumkit" drummers, and something that separates great drummers from good drummers is their ability to maintain intricacy in the separate parts while keeping the whole.
In electronic music, the artist is free to program as much or as little percussion as they see fit, (and usually opts for the much option), and almost always performs the function of a "groove", created by sounds that regardless of their actual source are still referred to as the kick snare, hi-hats, crashes etc. Electronic music is at the opposite extreme from group drumming: frequent variation in the parts, and changes to the groove is determined by how much the artist wishes to do it, and the longer pre-programmed (rather than live) electronic music has existed as an independent genre, the more the musicians take advantage of this complete freedom in their percussion arrangements.
In summary, even in classical music that includes large percussion sections, those musicians are not performing the same role musically as the percussion is in much of modern music. The qualitatively different (and more prominent) role of untuned percussion in modern popular music is something which has its genesis in West African drumming, and the influence of West African music on the music of the Americas (both north and south) as a consequence of the slave trade, and subsequent incorporation into to global popular music traditions of the 20th century.
