I've been a shop rat for 20 years and I might add a couple of points:
A 3/5 minute job doesn't exist. In no shop I've ever worked in has a job taken 3 minutes. It takes longer than that to get a name, phone number, bike type and issue, entering the bike into a booking system, and checking for parts. That's not even the mechanic touching the bike, that is someone like me booking the job in. I have NEVER Worked in a shop where someone has walked in, handed a bike to a mechanic, and walked out five minutes later having paid. If that's your expectation you should probably look in the mirror. I HAVE seen mechanics work overtime/after close to fix bikes for customers who are happy to leave them and have legitimate problems, to get them back on the road.
Like the others have said, when you have 150 of these 5 minute jobs, you have to draw a line somewhere. Our workshop booking system is currently booked at 300% of capacity for the current week - it has been that way since around April last year. Our shop has space for around 250 repairs and has been overflowing since April as well. Our lead time to book repairs is around 3 weeks, so your five minute job is pushing back the repair of someone who booked their bike in for service weeks ago and has been waiting. Routinely pushing back customers who have been waiting is (CAPS LOCK) BAD BUSINESS PRACTICE. Managing expectations is part of our job, and telling someone they may have to leave their bike and we'll try and squeeze it in rather than doing it on the spot is quite often the best we can do, and we'll be tripping over your bike till it's done because we don't have any more storage space.
On an unrelated note, we can also spot problem customers a mile away. It's just experience in dealing with the public.If you are having problems with every shop in town, it might not be the bike shops' fault. I'm in Australia, where robust verbal exchanges are expected, so ymmv, but maybe check the attitude during a pandemic and realise that having to wait for your bikes to be repaired may not be the most serious thing people have to deal with.