It's probably because whenever spellcasters are being compared, a Wizard comes in and says something like "we're the only ones who had to work for our magic", as if finding a powerful entity and convincing it to make a not horribly skewed bargain, learning to commune with the land itself, or following the orders given by a deity isn't "work".

And don't Bards also have to study their magic?

Wooing and banging everything that moves is hard work

I would argue that a bard has to work at it since they had to take the years to learn a musical instrument and then put it to use as an adventuring tool.

I make absolutely sure to talk shit at wizards every time I play a sorcerer. It's the way.