* You can find VTC licenses for ~60,000€.
* Uber and Cabify don't own those licenses directly but their CEOs and investors do (https://www.elmundo.es/cronica/2018/08/05/5b659a44468aeb9a29...).
The reason VTC licenses are expensive is that it were first illegal, then EU forced legality with a directive, then government found a loophole to forbid them again, so there was a window of a few years when they could be obtained.
So artificial scarcity.
Edit: Oh and BTW it was taxi drivers who mostly benefited by the price boom. They bought the licenses for less than 200 and sold them by thousands.
* What do you mean by "concentrated in very few hands (mainly Uber and Cabify)"? Surely Uber and Cabify don't directly own those licenses, right?