I think the point is that "only a few companies create these things" has always been true.
You need to provide a compelling argument why it is different this time.
The counter-argument is pretty basic:
RAM companies are currently selling as much as they can at high prices. This leads to investment in building new factories.
At some point the supply of new RAM will match the demand for it. When that occurs companies can increase profit by cutting prices to gain market share.
What's more, all the RAM companies have slightly different estimates of what the demand is. This leads to different levels of investment in new factories. Some will over-invest in new factories and the only way they can make their investment back is by increasing market share.
The final factor is new entries in the market. Chinese RAM manufactures can already produce DDR4 RAM (but only small amounts of DDR5). They can both increase supply of DDR4 RAM and are aggressively chasing DDR5 capabilities.
TL;DR: The profit motive is too strong for companies to artificially keep prices high once demand drops.