It's highly like just because they simply don't see that much demand. If they accepted bitcoin, probably sub 1% of their userbase is going to use bitcoin. And volatility shouldn't even be a problem, because bitcoin payment processors that automatically converts the bitcoin to fiat at PoS already existed since forever.
There's also a chance that they're trying to dodge potential problems with the government, but it's highly likely to be the former.
That's certainly true, mate. Fiat still has a lot of users, compared to Bitcoin. Amazon's user base consists mostly of customers who pay in credit/debit cards. Despite Bitcoin's popularity, the cryptocurrency is still lacking mainstream adoption. Not only that, but the slow transaction confirmation times and high fees makes Bitcoin a terrible currency for daily payments.
Retailers like eBay and Amazon want something that's fast, cheap, and easy to use. So far, Fiat (either through debit/credit cards) is "King" when it comes to making transactions instantly at a fraction of the cost. The Lightning Network aims to solve most of Bitcoin's problems, but it's quite difficult for the average person to understand. It's unlikely online retailers will adopt Bitcoin anytime soon. Just my thoughts