If Real Madrid were a company owned by shareholders, like most other clubs, that would make complete sense, but it´s owned by its members, and all profits are re-invested back in the club, not shared out. Whether the club is a money-making machine like now, or a black hole, like it was in the 90s, we´re still not going to see a single euro either way, so that means we, and consequently the president, who is elected by us, don´t care much about balance sheets.
We have more than enough money to sign M´bappé anyway, seeing as we haven´t signed anybody expensive since Bale (James´ price was offset by the sale of Di Maria), and I don´t think he´s ready just yet to carry the weight of Real Madrid on his shoulders. Meanwhile, Ronaldo is, now that he´s learnt how to pace himself, the best finisher in the world, and he´ll likely remain so for at least another couple of seasons, at around the time that M´Bappé is ready to take on the mantle.
130 or 150M euros for a 2-year loan? Yes, stupid anywhere else, of course, but not for us.