Premise: All cover bands play the same [choose your number of] songs.
Argument 1: People want to hear songs they know (“familiar” songs).
Argument 2: There are only so many songs out there that we can play and people want to hear or dance to.
TL/DR: Look beyond your ossified set list! Learn some new-to-you music!
OK, Professor Google offered me a shot at some Billboard Hot 100 data mining. From 1959 to 2019 the average number of songs on the Billboard Hot 100 is 461. The greatest number was 740 in 1966 and the fewest was 288 in 2001. The total number of songs was 28100 but we know there was overlap from year to year so let’s say 25% overlap from end of year 1 to start of year 2 and 25% year 2 to year 3. That’ll cull the duplication and now we have 14050 songs in 61 years. OK, 75% of those were crap songs so now we’re at 3500 songs (rounding the number for convenience). If you’re in a typical cover band that won’t play what they don’t like then we can knock off another quarter of that bringing us to 2625 songs to choose from. If you’re really a curmudgeonly lot we’ll knock off half so there are “only” 1750 songs to choose from. It’s a good bet the audience will recognize nearly all of ‘em and like most.
Even if you just play songs of the recent 25 years and ignore the 60s, 70s and 80s, that’s a lot of songs! Just how long ARE your set lists? If your band is playing the same songs as the other bands around your region it’s either because those songs are in high demand or none of you bothers to stretch out past your old set lists.
Of course this ignores personnel with personal problems and interpersonal or band dynamics/politics and that’s the OP’s point. YMMV
In case you want to play with numbers here’s an article
Hot or Not: Analyzing 60 Years of Billboard Hot 100 Data that’s readable. He also links to his source data via a programming geek.