We were encouraged to perform the same material every week if that's all we had. I think that was seen as better than having nothing. Maybe, in the long run, it wasn't...

I'm not a singer, but I'd guess that learning a song that you were perhaps going to accompany yourself on, sufficiently well to do it with without artificial aids, is a bigger ask than learning a new tune. I'd also add, speaking from the bitter experience of more than a few train-wrecks, that you can THINK you've learned a new piece well enough to get out there and do it, then, as soon as you get in front of people...