I partly agree...they do seem to get more confident about their world, but also, their body gets bigger, more cumbersome to try to get in & out of most hides.
For the most part, I've only kept the one large BCI (& for many years), & when she was large I hit on the idea of making her a more suitable hide than I could find to buy.
It was rectangular & flat as many are, but one thing that I did very differently (besides making it relatively longer) was to put TWO doorways side by side at one end: once these boas get "older" they also get more heavy-bodied, & it's just a hassle for them to go all the way into their hides with one doorway. I was delighted to see that my BCI seemed to enjoy her newfound ease of entering & leaving thru her "double-door mansion"...I watched with a smile as she easily cruised her cage, passing herself coming & going thru the doorways. She seemed to be having fun, & she quickly settled into using the hide, both deep inside, and on top for basking.
Just something to consider...Maybe my boa was aberrant in this, but it makes sense to me. Boas are not so shy (as some other snakes) that a double-opening feels too exposed...at least my big girl sure wasn't. But imagine yourself in their place, a long but hefty body trying to turn around inside a hide that only just fits them, you'd get tangled up inside. I liked the idea that once it was easier for her to move around in her cage, she did exactly that...which I think is healthy for a captive snake- a bit more exercise for good muscle tone.