I have a dropdown on my member search that shows all member groups, Pro support told me I have to use secondary groups instead. I just need to understand.

Note: I have the ultimate members plugin

I have about seven groups. When logged in as an Admin, I can see all the groups in that dropdown; when I log in as a regular user, I can only see two of them. 

By using the secondary group instaed of primary, I have buttons instead (of dropdown) that users can use to search. It does not look clean. 

Can someone explain why that is happening, or have a solution?

see attached

Thank you!