Why isn't he burrowing??

[Toothless]

Toothless has been in his enclosure for about 2 weeks now, and he still has not started a burrow! Instead he prefers to sleep under the shelf on the bottom level.
The soil does hold a burrow, and I've even started one for him, but still no luck. The soil area has lots of cover, so I doubt he feels exposed.
What else can I do to encourage him to burrow or what things can I look into that I may be doing wrong?
Soil is well tamped down and clumps nicely.