If bolt(s?) come loose it means tension didn't suffice, a possible cause is something lubricating (too well) between the threaded connection.
If that is the case, and it has to be there, a solution is to check and retension if needed, until the loosening stops, meaning that the lubricating stuff has been pressed out.
Dealers, or anybody doing it for somebody else, can't do it like this because can't expect the being helped to do this, so they use threadlock as a one time direct solution, and ofc no grease.
A combination is possible though, put some threadlocker over the first threads, then grease over the later coming.
That's what was done on my avatar bikes rear cog bolts, fine, but it was a drop red loctite on the first threads, resulting in some damage there when unmounting so I had to tap it out first to repair those threads, in order to replace the bolts with longer ones of specification length.