Circumventing shadow bans is fairly annoying to handle correctly; you have to get a KNOWN clean account (which if it gets shadow banned, becomes useless without notice) and verify other posts. You have to wait some time after your post to avoid racing issues and there is some other tricky timing issues that means that this will heavily slow down any post (I mean, you already have to now check if your post went through, that's atleast 1 additional connection).

This can also be easily spotted and combatted by using a half-shadow-ban for accounts that are seen repeatedly browsing threads that just had a shadow banned post made; the user will not see random shadow banned posts, making detection even more difficult as you have to now cross reference multiple accounts.

You can make it arbitrarily hard to circumvent shadow banning.

It's for the better if they discover that there's a shadow ban mechanism is in place. This acts as a deterrent.