Are geirim not frum?
While “frum” is an elusive title, I see where you’re coming from.
My guess is, anyone who comes into the fold, must at some point or another had a “jewish element” in their past, in one form or another. I can’t name specific cases (cause I’m not G-D) but from the reading I’ve done, it could be an 18th generation child from someone who got swallowed up in a mixed marraige, or something like that.
So, despite having a title to wear on his (or her) lapel, they do come from a gadol of sorts. Maybe not the kind that bios are written about, but a gadol in their own way (again, not G-D, so I really can’t say for sure)