pg_stat_all_tables: n_live_tup column value not persisting

I'm trying to get the row count of each table in a database, for which I'm using the postgres  statistics table:pg_stat_all_tables.

To determine the count Im using n_live_tup column in pg_stat_all_tables.

 I manually ran vacuum and analyse on the database so the latest counts get updated in pg_stat_all_tables. The issue is that after 3-4 days, I observed that the n_live_tup values for all the tables became zero in pg_stat_all_tables. I'm unable to understand why they became zero.

I did not  make any DML changes nor did I  run the pg_stat_reset function.

Pg Version: 12

OS:Linux 5.10

Thanks,

Pranavi