there are a lot of payment providers. what features do you like about Stripe that keeps you with Stripe?

If you use them for subscriptions you are effectively locked with them. The cost of migrating to a different provider (including existing subscriptions AND payment methods) plus the risk of something breaking the renewals is too high for most companies.

Are there any good Stripe Connect competitors? I haven't found any.

Zoneless is an open-source Stripe Connect alternative

Only Stripe offers a service doing international VAT for you.

Isn't that largely the selling point of every MoR? Paddle, Polar.sh and so on.