It is fairly simple to
It is fairly simple to understand. When they finally realised they would have to teach the AI to react to the outside environment like a human in both recognition and cognizant reaction they realised that having humans trying to label whole human reaction events was going to take decades.
So they built one of the most powerful computers in the world, from the ground up, silicon and all, then started teaching it how to teach an AI to learn.
This all takes time. Both getting it wrong and realising the problem. Then working out how to fix it and building the fix.
The question is not how long it has taken Tesla to get here or Why it took so long. The question is "when will their competitors realise they have to do the same?"
This will be an Entirely different market in 18 months.
The second question which is never addressed is. "When will the regulators catch up". Because the one thing Never talked about is the rather casual reference to the fact that FSD, even fully working and exactly as sold, is illegal to use correctly until the regulators approve it.
Nobody ever seems to talk about that little caveat in the documentation on FSD.
In some ways it may prove a harder nut to crack than self driving itself. Especially in the EU.