This is due to its flagship position and investors over the years have been paying a premium. It has come down over last year compared to its historical average due to Fed tightining.
As for management fee, consider it as operating cost of running the fund. You still get 10% dividend as distribution is paid and calculated after they take out operating expenses (including management fee) from the income.
Of course, you could argue that if the management fee is lower, you would have had higher dividend payout, but 10% is already pretty good
