Clone/pull slowly

Gitlab 13.12.4-ee omnibus.

Clone our project is slow.And I found the repository have 400+packfiles,nearly 20GB.
The idx file mtime is different from pack file.

I don’t know is it the reason of the slow pull.
And why the housekeeping task doesn’t cleanup the old pack?

This project has 230000+commits and 9000tags and branches.