Most of the players want to join Real Madrid because Real Madrid is able to build the future of the players.
Real Madrid's task is to find a good talented player to make them efficient and attacking enough. Most of the players that Real Madrid have signed to their team so far, they have managed to make most of them very skilled and good at their respective positions. It would not be wrong to say that they invest in talented players because after developing talented players enough they sell the player to another club for a huge amount of money which would not be wrong to call them a financial boost.
I think it's quite important to remember that they are quite loyal until very old age as well. Doesn't mean you will have a guaranteed job after 35, you may or you may not, but plenty of players got there and played for over a decade as well. Depends on how good you are of course, you can be like marcelo, ramos, kroos, modric and basically make a whole career out of it and could be good there, or you could be like bale or hazard where you barely ever play and then leave.
I think it's quite important for people to realize how good they are before they go to Madrid, you may get an offer, but accepting it just for accepting sake would make it terrible for you and you will end up with a very bad result and your career would be over if you are not ready.