what makes a d&d sub race stick?

[Unoriginal]

over the decades we have had many sub-races or alternative options like the 20+ types of elf and multiple types of nearly everything else.
with the new D&D version, a whole bunch seem to be getting cut for dwarves and halflings for example.
this has made me ask myself what makes some options stick and others not.
do you guys have any ideas as I am stumped?

People generally like options that stand out to be interesting while still fitting in the existing setting/lore/aesthetics/thematics, and they generally prefer when the species come with significant mechanics.

As a result, there will generally be fewer fans for the 15th type of elves introduced, which got a couple bonuses in snowy-terrain-related situations, than there will be for the 3rd type of gnome, which got some psionic powers, to give an example.

Sometime it's pretty clear when the devs are being lazy, out of touch or uncaring about the lore or mechanics, which will often get the option blasted into oblivion.