Some people just make the same character over and over again. While everybody entitled to have fun in their own way I found that long-term interest dwindle a faster in these players as at some point they just wind up doing the same things again, and again.
If you try to ask them or try to require them to play something different they wind up not coming at all. I had players wanted to play nothing but elves who had Silver in there name, another guy who named his characters alternatively either Alec or Marcus
My trick for overcoming this was to "give up" and let them have their way in the character generation. However in my Majestic Wilderlands setting there are clear tangible benefits to having a fleshed out background. Here is where I sneak in stuff that I hope get them to move beyond the one character they have been playing. I try to ensure that the background is different for every version of their character.
So the Silverring turns out to be a vastly different character than Silverwing. The same for the 1st Marcus against the 2nd Marcus. Because their initial circumstances are different resulting a different experience with each character.
After about two or three iterations of this the players began to think of other possibilities to play as the different experience expose them to different ideas about what they could play.
P.S.Years later we found out the second guy named one of his kids Marcus. When
we teased him about it, he turned red and asked us not to tell his wife about it as she didn't know the source of the name.