I think it is because on Mastodon favorites don't mean much besides showing some appreciation for the post. On the other hand, the Twitter algorithm would make posts with more likes more visible, but not as much as retweeting. So if you want to make a Mastodon post more visible you have to boost it

Favorites saves them as a favorite. Unless I'm going to want to see that tweet again in the future I don't generally hit the favorite button.

If I think it's entertaining I'll boost it for other people to see. There's no algorithm sorting things by engagement, so favoriting doesn't expand visibilty on boosting does that.

Iirc it’s due to the way federation works. You can see the real number of boosts but the favourites only show the amount from people who are on the same server as you. It’s not reflective of the real number

Mastodon has no algorithm, instead the users determine what spreads - so boosting posts is what helps them be shown to more people.

Favoriting a post on Mastodon doesn’t show it to your followers, so it doesn’t contribute to the “algorithm” the way boosting a post does. But it does tell the creator that you liked their content!

Usually it appears that way (like I was surprised some posts had 0 likes/favourites), but when I click on the post or go to the original source - it shows a higher number.

I just assumed that instances don't automatically gather likes as readily as boosts.

Favorites are like a nod but not visible beyond the conversation. Boosts make the post available to every one in your timeline. So if you think it’s fun, funny or worth other peoples time you should boost. I usually reserve favoriting for comments on posts I’ve already boosted.

Because people want that their followers see what theycfound interesting

favorite? on the web ui its marked as "save" likely part of the difference you are seeing.