The thing is, I don’t think D&D misses faction play because of the designers. I think it misses it because it’s not what players wanted. If you look at the 5e core rulebooks from 2014 and the early adventures and the Adventurer’s League organised play, they seem to be pushing their 5 Forgotten Realms factions pretty hard. The Zhents and Harpers have a long and storied history, but the Emerald Enclave, Order of the Gauntlet, and Lord’s Alliance are much less well attested prior to 5e. But the community never really seemed interested in this aspect of play, and I don’t think WotC kept it up after very long.
The thing is, I don’t think D&D misses faction play because of the designers. I think it misses it because it’s not what players wanted. If you look at the 5e core rulebooks from 2014 and the early adventures and the Adventurer’s League organised play, they seem to be pushing their 5 Forgotten Realms factions pretty hard. The Zhents and Harpers have a long and storied history, but the Emerald Enclave, Order of the Gauntlet, and Lord’s Alliance are much less well attested prior to 5e. But the community never really seemed interested in this aspect of play, and I don’t think WotC kept it up after very long.