supply and demand
I'd just like to point out that supply and demand are rather the opposite, i.e. workers are a supply of labor and businesses are the demand of it from an economics point of view, being wages the price they have to pay for workers time.
In this times we are now it seems supply of pilots has grown so much that it can provide such a big amount of labor demand is not asking for that negative wages appear, thats it, paying to work.
Thats what basic economics could explain, but i'd like to point out that the ones that pay for their type rating are predominantly those who think this way they can jump up the experience ladder getting a job that would take them some years to obtain otherwise.
In no way i'd like to sound any offensive to anyone, just to point out my thoughts. Paying for one's TR is a very rational decision once you prefer getting that job than the 30k€ it will cost you, so I wouldn't blame anyone on this, its a personal decision. When it comes to people who prefer having those 30k€ than a jet job or that don't have themanyways, its likewise acceptable in my opinion. Its a matter of preferences.