Nothing to worry about, in my opinion.
Mine does the same thing. I have not seen him (SEEN him myself) on his hot spot for a couple of months, and my temps are almost identical to yours (79F and 90F).
But he's active at night, hides during the day, eats like a beast, and drinks like he should.
On a side note, my corn snake also doesn't use her hot spot, so I don't think it's anything concerning either. Some might not require it all the time or very often - I'm thinking if your home temperature is steady, as mine is at about 74 or 75F, they might not be all that chilly in their warm tanks. But still important to give them that option of a gradient!
Reply With Quote