I think we talk about hundreds and maybe even thousands. There are 372 exchanges listed on coinmarketcap right now and I believe most of them running their own node.
I definitely hope they are. Is 372 nodes enough? In the theoretical scenario of 1 CPU 1 Vote, the number of nodes would've be in the tens of thousands. Businesses don't usually run their own node, at least from what I've observed, most are using either coinpayments.net and bitpay. It's way easier to have a service do the payment for you.
Any Bitcoin Core wallet is a full node actually. I have one. And also run bitcoind on one of my servers. It uses about 300Gb of disk space, but I'm ok with that. It's affordable. TRON full node consumes much more resources for example.
IMO, disk space and internet bandwidth is scarce for the average joe. When alternatives like Electrum and other SPV wallets exists with little to no synchronization needed, most would choose them over a full node.
When alternatives that are better than running a full node exists, the average user won't run a full node. The tangible benefits is just too little.