Query choosing Bad Index Path

*Postgres version:* 11.4

*Problem:*
Query choosing Bad Index Path. Details are provided below:

*Table :*

*Doubt*
1. Why is this Query choosing *Index Scan Backward using table1_pkey
Index *though it's cost is high. It can rather choose
BITMAP OR
(Index on RECORDID) i.e; table1_idx6
(Index on RELATEDID) i.e; table1_idx7

Below is the selectivity details from *pg_stats* table
- Recordid has 51969 distinct values. And selectivity
(most_common_freqs) for *recordid = 15842006928391817* is 0.00376667
- Relatedid has 82128 distinct values. And selectivity
(most_common_freqs) for *recordid = 15842006928391817* is 0.0050666

Since, selectivity is less, this should logically choose this Index, which
would have improve my query performance here.
I cross-checked the same by removing PrimaryKey to this table and query now
chooses these indexes and response is in 100ms. Please refer the plan below
(after removing primary key):