It's not quite that easy. Have you ever tried it? See my post below. Basically, yes, I've done it, but i had to go through a lot and was lucky enough to even get them to listen to me. I just happened to know the right person to get me through. So, super lucky there.
Furthermore, they have an AI that takes you off the whitelist if it sees your bot 'misbehave', whatever that is. So if you have a certain kind of bug in your spider, or your bot 'misbehaves', whatever that means is anyone's guess, then you're going to get kicked off the list. So then what? You have to try to get on the whitelist again? They have Bing and Google on some special short lists so those guys don't have to sweat all these hurdles.
Lastly, their UI and documentation is heavily centered around Google and Bing, so upstart search engines aren't getting the same treatment.