This isn’t as much about stopping middleboxes on your perimeter that you fully control, but a lot about middleboxes between you and the destination that are outside of your or the destinations control.

Those are often used to add ads rather than block them.

If you yourself want to block ads, do so on your machine (where traffic has already been decrypted) or on your router (which will then decrypt traffic for you and re-encrypt it with its certificate that you have added to your machine).