They actively prefer keeping confortable margins than competing between each other. They have already been condemned for active collusion in the past.
New actors from China could shake things up a bit but the geopolitical situation makes that complicated. The market can stay broken for a long time.
Rapid increase in capacity leads to oversupply which leads to negative margins. They've been there before, and they don't want to go there again.
RAM manufacturers do routinely setup new fabs and decommision old fabs. Maybe they're trying to hurry up new fab construction in times like these, and they would likely defer shutting down old fabs or restart them where possible. But they're less likely to build new fabs that weren't already part of their long term plans.