I am not privy to the discussion about whether to include them on old worlds, but it is highly likely that old worlds would have died quicker if they had been.
Consider some worlds have been around for 3-5yrs or maybe more. Only 100 or less accounts remain logging in on some old worlds out of 30 000. The substitution rules especially would have hit very hard on these worlds. Why, because out of the 100 accounts logging in it is maybe 30 or less players with substitutions that have been active for years. Even if the substitutions continued the original owners are often no longer playing the game on any world so aren't contactable for them to re-substitute every 30 days.
Some would argue that these worlds should be closed, but for whatever reason, EA/Envision don't publicly support the closure of a world (that's why the Vet servers continue after the end of their season).
The loot changes probably wouldn't have much effect on very old worlds where many are at level 65 for 30 or 31 bases and can kill any forgotten with one shot, probably even the fortress with one player if they could get the level down with the injections. On more recent worlds (the tib, firestorm and wrath series) where multi-accounting, pre-hitting etc was rife when the worlds started may have been adversely affected. However, as this is the purpose of the loot feature I don't understand why it wasn't included on all worlds.