People regularly make dozens of accounts to downvote a single image, create a new account each day to send a PM each day to the target of their butthurt over a single comment 7 years ago, set up different accounts to mass vandalize tags hoping the account switching won’t trace back to their main,…
Forcing account creation for simple site interactions would only inconvenience legitimate users that don’t feel like setting up an account for a pony image site just to say “this is cute!”; on the other hand anyone with bad intentions will not be deterred one bit by the extra few seconds, and the most moronic of them all will have been guided into having an account which now makes their shitting up of the site a whole lot easier for them, and not one bit easier to moderate.
Just because you have a strong opinion on something doesn’t mean you’re right about it. You may have a lot of experience in being an asshole, but the site mods have a lot more in dealing with them.