When I'm signing up for one service, I don't want to have to sign up for another service, no matter how easy it is. It's not a question of difficulty, it's a question of convenience.
That's why services like Firefox Relay exists. Just generates a new email address for you whose inbox gets relayed to your regular email, no fuss needed. I don't personally pay for it but I do use the heck out of the free email addresses they provided.
I have such a hard time understanding why people think e-mail addresses are some kind of special thing hard to come by.