Space marine chapters have special characters, unique tactics, special models and all that for variety. There's a mechanical and modeling difference between Green Robe marines and Red Angel marines and Wolf Wolf marines. Not so much for Dark Eldar.
If you had the same treatment given to Dark Eldar Kabals you'd see more people play as specific Kabals. Marines have variant chapter tactics so with Dark Eldar I can see variant Power From Pain's being what makes Kabals distinct with their own special characters and colors, representing how each has a unique way of channeling the power of pain:
*Vect's Black Hearts being the Utter Arrogant Confidence Kabal so as the pain builds up so does their Ld and coordination to deepstrike reserves in flawlessly
*Shooty Kabal who's shards and lances are as hungry for souls as they are (ignore cover, +BS)
* Stealthy Kabal that turn pain into darkness (stealth), the screams of the fallen blacken the skies (nightfight at turn X)
* The Wraithkind: phasing in and out of reality due to Vect's hilarious prank involving shadow monsters, they gain an inv sv instead of FnP, able to go into reserve and deepstrike on turn X
* Malys's Poison Tongues: They turn pain into doubt and confusion among enemy ranks, penalizing their reserves, forcing enemies to move as you want to on turn X
* Duke Sliscus's Sky Serpents have poisons that get stronger as more PfP is gathered
But as long as there's no mechanical crunch to make Kabals distinct from one another, Dark Eldar players won't really care much about how they paint up their dudes.