Why is this option disabled

Yes, you can. You can also drive over the speed limit by default, or kill people by default. But just because you can doesn’t mean you’re allowed to, and that you won’t be punished when you’re caught doing it.

The rules are simple: no more than three free hosting accounts per person.

Yes, we are aware it’s possible to sign up multiple times with different email addresses and circumvent the limit. That does not mean that you’re allowed to.

I was just going to give you the warning and let you go about your business. But seeing how you seem to proud of breaking the rules, and because you already had a large number of your accounts suspended for spam before, I went ahead and took down about a dozen different accounts you have.

Go find another hosting provider. We don’t do business with spammers who abuse our services.