The issue is they've never done it before and are scared of domain squatters. They don't want everyone to just create whatever tld they come up with so they keep costs high and will do research before accepting things, limiting it to companies who have copyright or some other reason to be the only ones who can own a name. And they don't want similar names out of fear that people will mistype something and get to the competition. For instance, if someone ware to register .apples then apple can't have .apple because its too similar.
They justify the huge cost to limit who can do it and in preparation of inevitable lawsuits from those that disagree with their decisions.
You can find all that info and more on https://newgtlds.icann.org/