1. Adds inordinate amount of time required before flight departure time.
2. Can't bring any food onto flight.
3. Requires secure section of terminal, typically without lounges or sufficient facilities.
4. Issues with immigration means you miss your flight.
And more...
Despite all these I would rather have pre-clearance.
1. and 4. are time issues, and I would much rather waste time before the flight and after. Especially when I travel with the kids, after 12-13h flights I'd much rather go straight to luggage pick up than wait for up to an hour at immigration.
2. Not relevant to me
3. Regarding the lounges perhaps they can have them before pre-clearance, and then an hour before boarding they call ppl from the lounge.
If I had US citizenship and global entry obviously I wouldn't want that