There is no other league with a team with that kind of monopoly of the top players in the league. Bayern can literally buy anyone from almost any team in Bundesliga. They can buy Dortmund players or just ask them to run down their contracts and leave for free.
You think Napoli, Roma, Milan, Inter, Viola would sell their top players to us? Fat chance. Juve was the best team in Serie A by far the last two years but not because of having a monopoly of the top players in the league, more so because Juve was a very well constructed team, and this, alongside a couple stars has allowed us to dominate on a very limited budget where we can't buy those 30mil+ players.
And don't compare Spain to Bundesliga. Madrid and Barca provide massive competition for each other. Dortmund provided that 4-5 years ago, so Bayern just used their financial muscle to buy their best players.