I think the big thing is people don't know how to put earplugs in properly, the entire plug should be in your ear canal. To do it, you need to pull up from the top of your ear when inserting to fully seat it.
Put an earplug in your ear that seals the ear canal, then press firmly on the outside of your ear canal (on the side of your head, in front of the tragus). Feel that pressure. Now imagine doing that for 8 hours a night.
I have had to sleep with ear plugs because of noise from neighbors. Two results: waking up with painful ear canals during the night, and semi-permanently enlarged ear canals, requiring the use of larger ear plugs to seal, which causes more pain.
If you can comfortably sleep with ear plugs with no adverse effects, you are lucky.
Maybe one day we progress as a society to the point where one's right to quiet isn't dwarfed by others' right to make noise. Not gonna hold my breath though..
What almost works for me is using two differently sized earplugs and putting the smaller one in the pillow-side ear, because the pillow pushing on the ear canal causes it to seal despite the smaller plug. But when I roll onto my other side several times a night, I'd have to wake up and swap ear plugs. It's not feasible. :(