Should they also start CPU fabs? Batteries? Lithium mines?
On the other hand, if Apple invests in RAM production and prices fall, it's not like the investment is wasted, RAM is a commodity. They lose at worst the opportunity cost of deploying the capital inefficiently, but they have so much that it hardly matters.
Apple should take this crisis as a warning that they aren't vertically integrated enough to protect their business model.
As for batteries, Apple is not even close to the largest consumer of batteries. If they were an electric car company then yes they should be making their own batteries.
Memory is well within Apples design and Engineering capability. Long-term, Apple has to think about the Chinese getting a bigger part of the market in memory because they can undercut the three company cartel worldwide in time with this fake AI memory crisis.