In the US a lot of the investments into these managers are from pension funds - each of which is a multi billion fund in itself. Think of NY firefighters pension fund, Canadian teachers fund etc etc. To compare something like that if you bring up LIC in india - their AUM is around the 600B USD mark for last year, which isn’t particularly bad when you look at the lower ones on the american list and account for our country being poorer in general.
Feb 2024 alone had nearly 50L new Mutual Fund SIPs registered in India - that’s a huge number and the trend for MFs is only upwards in india.
Blackrock also owns a lot of Real Estate which we don’t have an equivalent of in india, the mutual funds are strictly holding Equity or Debt or Cash of some form so it’s not quite and apples to apples comparison. Same for the other names there (except Vanguard)