How much are they being paid? $500 per week? $200 per week? $50 per gig which happens three times per year? You have to align expectations with what the gig is paying. There are a ton of other things happening in life so a band that pays effectively nothing becomes a lower priority. Chose songs that are easy crowd pleasers.
Exactly my point with the James Brown anecdote. I see a lot of threads on TB along the lines of, "why aren't the unpaid amateurs in my hobby band acting more PROFESSIONAL?"
We're all busy people. Not all musicians are perfectionists. A lot of amateur musicians look forward to "band night" as an opportunity to have fun in a casual, criticism-free environment. If you are the bandleader, and you want your hired guns to show up, on time and well-prepared, having done their homework and transcribed their parts note-for-note, then your side of the equation is to pay them a professional rate.
If on the other hand, you can't afford to pay your musicians for rehearsals, then my advice is to write out some accurate, easy to read charts. That way they aren't wasting your rehearsal time trying to remember how the song goes, and you aren't wasting your unpaid volunteers' home/life/family time by giving them homework in between rehearsals.