They had built way too much capacity during the 90s and were losing money on every chip because they couldn’t run the fabs at full capacity. That’s why they colluded to increase the price to save their collective hides.
A new competitor wouldn’t be able to enter the market and lower the prices without also losing money. That’s not the case today, the Chinese are trying hard to do just that.
Conspiracies have been documented enough times that it is totally valid to surmise that there's one in place at any given time, about any given field.
A quick inquiry to google on 'proven conspiracy theories' returned ten results just on google's AI. And it left out Iran-contra -presumably for the sake of brevity.
Sorry, to think there's a conspiracy isn't so whacky and unhinged as people want to make it out to be.