I was thinking pretty much the same things.Maybe they just need more candlelit dinners?
Only thing that comes to my mind is about the "proven" female- how many times has she reproduced in the past & how often? Her body may simply be "done" or needing a rest? Just saying "proven" can mean almost anything? And it doesn't mean she's currently ready to breed- obviously. (I've never bred BPs, btw, but have bred other snakes.)