Because it doesn't make a difference, because `SELECT 1` doesn't need to touch the database:
Running 100,000 `SELECT 1` queries:
PostgreSQL (localhost): 2.71 seconds
SQLite (in-memory): 0.07 seconds
SQLite (tempfile): 0.07 seconds
(https://gist.github.com/leifkb/d8778422d450d9a3f103ed43258cc...)