why does this GIN index not used

  
QUERY PLAN

1
Bitmap Heap Scan on tmp_t v  (cost=1049.31..1522.75 rows=169 width=36) (actual time=8.509..8.509 rows=0 loops=1)

2
  Recheck Cond: (o @> '[{"accession": "nm_001178208.1"}]'::jsonb)

3
  ->  Bitmap Index Scan on idx_tmp_t  (cost=0.00..1049.27 rows=169 width=0) (actual time=8.506..8.506 rows=0 loops=1)

4
        Index Cond: (o @> '[{"accession": "nm_001178208.1"}]'::jsonb)

5
Planning time: 0.238 ms

6
Execution time: 8.566 ms