Moderators can assign and remove the expert title. It's not automatic.
You're basically asking to make Experts into Editors. If we wanted or needed more editors, we would ask to promote more editors (which we will do soon!).
Expert exists as a "I have put a lot of knowledge and time into the Pokebase and now I can edit content as a reward / to help more!" title. In that it's supposed to be low stakes and anyone can achieve it.
Editor's are curated and trusted by the site admin. The entire purpose of Editors is that they're trusted specifically enough to be allowed to use the admin section.
What I'm trying to say is that you're basically asking for the removal of either a.) The role and function of editors or b.) The standards and quality assurance of (what would then basically be) editors by allowing practically anyone to perform that role. Even if we could just not promote someone to Expert to prevent then from using admin...then would we create a new title to reward people who hit 6000? What would the point even be?
And then we would have to go back through every single already existing expert and deem them worthy or not.
Tldr users are promoted to Editor if we think they're qualified and we need them. Transfering powers to experts means that they won't necessarily be qualified or trustworthy and creates other issues too.