It is stupid easy to get a free .edu account. It will not hamper spammers in the slightest. Even if they don’t want to make a few .edu accounts a day to do their spamming, they can just buy .edu accounts in bulk for about 10 cents per. No one is making thousands of kbin accounts to spam from, they make a handful a day, and use them till they get banned. Then they make a few more.
.edu accounts are a terrible way to try and prevent spam on kbin. There is literally an industry around generating fake .edu accounts. You can buy them in bulk. Some colleges receive 10’s of thousands of fake applications a month trying to get free .edu emails.