alt Hacker NewsIDK man .. many services really just don't even want to deal with a sign up they are never going to reach. By using a disposable email, you're telling the business, I want to use your service, get value, but I don't really want you to reach me. To them, it sounds like a loss loss situation. Business are there to make money, and they offer a signup/trial/free account so they can give you access in exchange for being able to reach you.
But I do sympathize with the stupidity of marketing email madness.
Aliases are fair game .. for organization for just hiding your own email to limit tracking.. that's fair .. but bad, known disposable email generally just costs too much and is too risky for businesses.