I wonder if the scripture was actually referring to eunuchs not being able to present bread at the table, instead of guys with actual deformities of their testicles. Maybe it was something about that, and that eunuchs couldn't have privileges, idk. Its just a guess on my part, could be wrong though.
I do know that eunuchs were a big thing back then. More so than today, I think. They would sometimes be in charge of different households, as a "prevention" against them impregnating the woman of the household, lol.
Maybe more and more numbers of Israelites were becoming eunuchs and they had to institute certain restrictions, like this one? Just a guess.