I think we always tend to look for guys/people that we want to play with, guys/that are good and seem like you can form a good band with, guys that you get along with so you assume will be good to spend time with creating a band, and all of these type of things. But what can be most important, is finding people with the same objectives as you have. The toughest thing is finding people who want to commit to about the same level on practice time, amount of gigs per month, etc., so that you can be on the same page with those things.
If you find great guys who are great players and you hit it off great with them, have a blast practicing, etc. but you want to gig once a month and they want to gig twice a week... it won't work, and vice versa. So the tricky thing is finding a whole group of people who meet all the first objectives, AND the second. Usually, the band tends to have a mixture of the various "qualifications" and that can last for a while, but not long.
One of my groups I played with had several gigs messed up at the absolute LAST minute, because one guy was "on call." We'd literally be day of a gig and on the way TO the gig and get a call that he couldn't be there. And it was legit. He HATED to miss and LIVED for the gigs, but after a while, we had to decide that he had to tell his boss he could not be on call on gig days any more or it wouldn't work. Mixing in younger musicians who have younger kids is another wild card.
In the end, it's just hard to find a group of 3-4-5 people who are all committed to similar levels of time and energy, have similar musical abilities and goals, and have similar levels of availability.
And then, to acknowledge your point, lets be honest here, the "target audience" for these musician and singer inquiries is perhaps a little flakier than the gen pop.
And know I don't mean all of "us" but an "above average" amount. But a lot of it has nothing to do with flakiness, it is just general mismatches in the availability/commitment levels. IMO
