> Why wasn't this there from the get go?

Even better, why was the AI feature ever added in the first place?

Quite a few of the LLM features actually add value for a certain group of users. Automated image descriptions for the visually impaired, automatic translation, ... Running those on local models is a net benefit for quite a few people, but they get a bad rep because they're "AI" and the current trend of shoving AI everyplace and with no means of escape means that AI in general has a - well deserved - bad reputation.

Because a browser needs users, and some people like AI features. Firefox can't win the battle, or even survive, on an AI hating, nerdy user base.