That assumes that
* it instantly brings them a ton of consumers * they have capacity to serve those customers
if they don't competitor can just keep higher price (especially if it is just small middleman fee most people might not care that much about)
And even if both of those are true worst possible case is them expanding to handle influx of customers and then competition following in few months, making their investment moot
That's true, but the thing about price fixing is that it basically guarantees these conditions.
The price is artificially high -> there's a ton of demand waiting to be unlocked by the "potential energy" gated behind the unnatural price
Capacity is easy to plan around; get too much and you can just raise the price again.