Set enable_seqscan doesn't take effect?

postgres=# SET enable_seqscan = off;
SET
postgres=# explain select * from t;
QUERY PLAN
-------------------------------------------------------------------------
Seq Scan on t (cost=10000000000.00..10000000023.60 rows=1360 width=32)
(1 row)

postgres=# select * from t;
a
-------
[1,2]
(1 row)