Both from a gameplay and a lore perspective, I don't really understand what the rationale for removing delta forks is.
From a gameplay perspective: the niche of "fork that's about as capable as an ALI" seems like a useful one to have filled, especially for fire-and-forget tasks where you don't plan on reintegrating with the fork, or where the fork is likely to die and players don't want to deal with the guilt of sending another sentient being off to die.
From a lore perspective, ALIs are canonically neural nets, so it isn't clear why a transhuman neural net couldn't be pruned down to the level of an ALI. Also, Fetches are still described as "a delta fork of a TITAN," which doesn't make sense if delta forks don't exist in the universe any more.
Having four types of forks instead of three doesn't make the system that much more complicated. What do we gain from taking that option away from players and making the setting slightly more incoherent?