1) Many parts which must be cleaned.
2) Often the parts are plastic, which is unacceptable combined with hot water (or any, really.)
3) The glass is very fragile, potentially leading to breaking and even injury. Usually top-heavy designs, too.
My FP doesn't have any plastic components in the filter area, only in the top.
Yes, I have broken some FPs, one by juggling it out of a high cabinet and one by scrubbing it too aggressively while soapy. Like someone said, there are steel presses available as well.
1) Agree, personally I am too lazy to clean it every time, just rinse it in water
2) Agree, though, everything in contact when brewing is metal or glass
3) Had my current french press for 6 years without issue.
Nonetheless, guess the difference boils down to personal practicality.
After cracking my umpteenth glass cafetiere (what you call a french press in the US), I bought a metal one - that was around 10 years ago, and it's still going strong!
It's easy to clean too, but then every one I've had has been.