There is an overarching reason for transposition of wind instruments, which can be corroborated by anyone who has played woodwind doubles in a pit orchestra.
Regardless of the reason transposing instruments came into practice in the first place, the practice is still standard in writing circles (besides the valid observation that there alr4eady exists a huge body of already-transposed repertoire) is quite simple:
Instruments transpose so that players of a particular instrument, or type of instrument, can play any of an entire family of their weapon of choice using the same fingering scheme.
For instance, modern clarinets come in a huge variety of sizes -- E-flat Sopranino, B-flat Soprano, A Soprano, E-flat Alto, B-flat Bass, E-flat Contra-alto, B-flat Contra-bass ... and even F Basset Horn (which is actually part of the clarinet family and is retained in the orchestral arsenal largely because of the large amount of music Mozart wrote for them). Interestingly, ALL of these clarinets use virtually the exact same fingering scheme, which allows any clarinetist to switch easily among the various varieties -- for an entire work or performance, just one selection, or even in the middle of a single work and back again. In addition, virtually all of the woodwinds are built on almost identical fingering methodologies -- with the exception of Bassoon (although the bottom register of a clarinet highly resembles that instrument's fingering structure). The Saxophone family is similarly varied, and the same fingering principles apply from one to the next. If you look at fingering charts for Flute, Oboe, English Horn, Clarinet and Saxophone, the note "D" is fingered in precisely the same way because the parts for these instruments is transposed to allow for this.
If the instruments were NOT transposed for the players, the same condition would exist as that for the recorder family. Although recorders are constructed almost identically except for their physical size, the fingering schemes for each of these is different -- BECAUSE the practice of transposition has never been applied to them. As such, in order for a Soprano recorded player to switch to Alto recorder, it is necessary for the player to learn and entirely different set of fingerings (and, in many cases, to learn to read a new clef as well).
The brass instruments are similarly described. The fingering patterns for brass instruments are identical between transposing trumpets and horns -- and since there are 7 different possible fingerings for a trumpet or horn which correspond to the 7 different possible positions on a trombone, the resemblance throughout the family is complete.
In modern practice, bass-clef instruments do not transpose ... but, in order for a treble-clef brass player to read music written for Euphonium or Tuba, the player has either to learn an entirely new set of fingerings or transpose the pitches into a different key in their head while playing. So many trumpet players have switched to Euphonium over the years that a B-flat, treble-clef part is nearly always included in wind band literature to allow for this shift.
One final note (pun intended): Many writers and conductors seem unaware of this circumstance, but if one plays the note "C" on any instrument, regardless of its transposition, the instrument will sound the note of the key in which it's built. The only exception to this is low-brass instrumentation -- which, since they don't transpose (see above) have learned a set of fingerings peculiar to their instrument in terms of pitch-level. As such, a tuba play can't play a trumpet or horn without moving the notes in his or her head to allow for this difference.
Finally, bass clef NEEDS to be different that bass clef -- in order for a conductor or keyboard player to be able to maintain the difference between registers while conducting or performing. A pianist or organist would be easily confused when reading down a page if all the notes were on the same lines; the beauty of a grand- or three-line-staff is that a player can keep a reference point because the clefs are vertically grouped and arranged on differing lines and spaces. If this were not the case, players would be much more likely to play wrong notes in wrong registers, particularly when sight-reading.