Some clarifications
Yes, mice often have dpi-switching mapped to hardware buttons. However, as with my mouse, this hardware switching offers very limited granularity and many dpi "modes" can only be selected in software by a proprietary driver.
I'm mostly talking about RTS games (think StarCraft) as well as some rhythm games (think Osu!) where persistent mouse behavior is essential to playability.
Competitive fps players actually often play at very low dpi on essentially barebones hardware (think Intellimouse Optical @ 400dpi) compared to what's out there. Because these older mice don't actually have any dpi switching functionality, they usually don't require any special mouse drivers.
This is also not about whatever special fancy macro buttons on the mice not being supported.
If you desire a consistent mouse experience, you almost always want to leave the mice at their optimum DPI value and you are very limited in choice.
RTS players tend not to care about this because they do not need the level of accuracy required to ping off headshots while moving, thus they're happy with "good enough" while manipulating DPIs in ways that'll cause all sort of sensor problems which could be a deciding factor in an FPS game.
If you care about having the best mousing experince you're really talking about using a deathadder, g400 and their kin. You are correct though, fancy macro buttons and high price tags tend not to get you the best mouse. But to think the RTS player relies on their mouse as much as the FPS player is folly.
I'm mostly talking about RTS games (think StarCraft) as well as some rhythm games (think Osu!) where persistent mouse behavior is essential to playability.
Competitive fps players actually often play at very low dpi on essentially barebones hardware (think Intellimouse Optical @ 400dpi) compared to what's out there. Because these older mice don't actually have any dpi switching functionality, they usually don't require any special mouse drivers.
This is also not about whatever special fancy macro buttons on the mice not being supported.