I'm pretty sure it's part of "the algorithm". I don't get 2FA prompts every time, but ever so often for it to be annoying - especially since I am then thrown back to the login prompt which dares to tell me that the password from my password manager was wrong. No, it wasn't wrong, your system apparently just cannot handle going from a password prompt to 2FA and then realizing that the correct password was already entered! I asked lots of people around me and they don't have this issue, so I guess it's kinda random who is treated how.
My own experience with using PayPal usually (as in: almost always) goes like this:
I get a PayPal popup that says something like "You're already logged in! One moment," and then once that goes away I push the whatever button corresponds to "Yeah, sure -- pay it."
It's generally a one-button operation for me, and has been for years.
