This was discussed on SN a while ago.

I don't think that the stores chose it for being trendy, but because it was good and very easy to integrate. Coinbase Commerce used to be a very nice self-custodial merchant solution to accept on-chain payments, but of course they had to screw it up with smart contracts and BS. Maybe some merchants just don't know much about the recent changes. Letting the merchants know might help make some of them consider other solutions.