Lol, La Liga only has Real Madrid and Barcelona as the richest team and after all, Premier League teams are the best when it comes to finances. Also, I am surprised when you say Serie A teams are without a lot of star players because after all, teams like Inter, Juventus, Milan and also Roma have a lot of star players and maybe there are other teams too. So, I don't agree with your statement and also, young and old players are always in every team and in fact, Real Madrid still relied on old players last season too.
Of the several seasons that have passed, we have indeed been served by two teams that have the ability to compete in the top rankings of the league, they are Barcelona and Real Madrid, even these two teams make Laliga even more interesting to watch every season. Indeed the finances of these two teams are the biggest in Laliga at the moment compared to other teams. These two teams always sign a lot of great players in every season even this season real madrid did it again by bringing in Bellingham.
So, from that point of view, I think every league from other countries also has a lot of stars on their team, such as Serie A, Ligue 1 or the Bundesliga so that each league has its own advantages in attracting football lovers. For that, I think Barcelona and Real Madrid are the two icons that catapulted the name Laliga for now. Sevilla or Atletico Madrid often surprise them, but they are still unable to compete with these two teams in Laliga.