Earlier quoted context omitted.
Having the actual url be completely different from the displayed url simply shouldn't be possible. Allowing that invites scams like these. At the very least, they need to be the same domain.
Yes! This is crazy to me. How can this not be a thing that has already been discovered and instantly fixed?
They might work for BigCo, but rather than have the ad point to bigco.com/product they instead have the ad point to tinyurl/bitly so they can track how many people click the ad and repoint it to another URL easily.
There is a whole industry of these redirection services that gather stats, direct users different directions based on mobile/desktop or country. It isn't rare to bounce a user via a whole chain of them.
To support all those users, ad networks have to allow the apparent URL and actual link target to differ.