In short, The answer is that most of the hard/precise/technical work is done by the right/dominant hand.
That is, the left hand is the “show-y” one, and the one whose motions are most obvious to the viewer. And certainly what the left hand does is important (for example, it is primarily responsible for intonation).
And all of this contributes to the common misunderstanding that the left hand is “doing the majority of the work”.
But all the other tasks responsible for the production of the notes (and the tasks requiring the most precision, agility, subtlety and skill) are the responsibility of the right hand; that is, rhythm, articulation, timbre/voice/volume/balance etc.
One way to think of this is to notice that in almost all cases, for each note played in a melody the right hand typically has to make several more motions for each motion made by the left hand.
There are some exceptions here. For example, in the case of pull off/on, trills, etc. But these are the exception.
On the other hand, for example in arpeggiation, it is possible to play long passages where the the position of the left hand does’t move at all.
All of this is true in the case of either flat-picking, finger-picking, or, for other instruments, bowing.
(In the case where the player is simply casually strumming the guitar, it might be true that the left hand is “busier” than the right hand, but I think we could all agree that this is not really the instrument in a serious sense.)