Yeah, I don't understand it either.

They had M2-P4, Stephanie-P4 and V2-P4 that were compatible with Dork and Posette.

Both as low and high res versions.

They had M3 to M2 and V3 to V2 (Could even use V2 textures), Aiko to SP3 and Hiro to David.

Luke and Laura to PreTeeners and Matt and Maddie to Preschoolers.

But then V4toV3 was the last fully functional legacy figure.

No M4 to M3 or M4 to David. No Kids4 to Matt and Maddie.

Genesis has legacy shapes, but they need DSON and aren't Poser 6 to 8 compatible.

 

Guess the marketing guys told them it isn't worth the effort.