I think lookahead is something that IS learned, but not really specifically learned through training. It seems like something that naturally comes along as your current pair becomes muscle memory, you can naturally switch your focus to the next pair.
It seems like you're describing that as if learning to look ahead is a subconscious action where, as you gain the ability to solve a pair with muscle memory, you just automatically start looking at other stuff simply because it is no longer necessary that you look at the pair you are solving. But if you aren't focusing, it's still really easy to keep watching the pieces you are solving even though you don't need to and never really lookahead at all. If you haven't yet learned to lookahead at a particular turnspeed on a particular puzzle, it will take a conscious effort to try to do so.
Here's the thing: there are some people here whose minds, for whatever reason, work in the right way for cubing lookahead to come very easily and naturally to them. They get fast really quickly, other people want to do the same and so ask them how they did it, and they say "lol I didn't really focus on learning look ahead, it just came as I did thousands of solves." But that's the very
reason they got fast so quickly, and it doesn't mean that
nobody should really focus on learning to look ahead. Such people are the exception to the rule. Unfortunately and counter-intuitively, those very-fast-improvers are actually some of the worst people to give advice to cubers struggling to improve.
For most people, if you are passively waiting for lookahead to just "naturally come along", you are limiting the rate at which you can improve. It's not just about "learning to look ahead," it's "learning to look ahead at a faster turn speed than you could before," and this more specifically-stated goal is definitely something that can be actively trained. Say you can successfully lookahead during F2L at 3tps, but no more. So you do a solve around, say, 3.5 TPS, actively attempt to lookahead, and can't because you are turning too fast. Then you keep doing more solves
still turning this fast, not being able to lookahead very smoothly, until you start to realize that it is getting easier. Then, ta-da, you have learned to lookahead at this higher turnspeed by intentionally trying to do something that was difficult for you. I would call that training. This is where the idea of metronome-training for F2L came from, though the metronome is really just a tool to replace (make up for) your own (lack of) ability to focus.