I've only had direct experience with three Colombian boas (a mature female, a younger male and a very young female). All three have occasionally burrowed even if they had hides and I've seen burrowing used as a way to ambush live prey too. I think it's just likely part of their natural way.

We do offer the boas good deep bedding to allow for this and the heavy female boa was on an aspen/double milled cypress bedding. Pure aspen was too light for her weight and tended to get packed down so the mix with the cypress created a really nice thick bedding for her that allowed heat through and also allowed her to burrow if she wanted to. The younger boas have hides and use them when they feel like it...sometimes they'll use the hide, sometimes they'll burrow, sometimes they'll just laze around on top of the bedding or on top of their hides.

Here's some pics.....

Severus, the 05 male tucked up in his hide this morning....



This is Sonja (aka Rauri) hiding her 6 foot self in her bedding. She actually scared the beejesus out of me because when I first looked in her enclosure she was completely hidden and I thought she'd escaped. I guess my bouncing around and moving her big enclosure disturbed her as she stuck her face out to check out what the crazy human was up to now. LOL