They can be very very fiddly.

They get contaminated fluid - presumably from shit cylinder seals. They can be difficult to tune (too much travel, not enough). They can be fiddly to change pads. The pistons stop working on one side (binding up), they can leak, etc.

Combine all that with an electronic, wireless gear shifter that’s in close proximity and the roadside repair in the rain can be miserable.

Don’t get me wrong, I like them a lot but most my shop visits are for brake repairs. I have to work on them every few weeks as I go though pads in as little as 6 weeks.