Why not use Snapshot isolation for everything read-only?

Suppose that: - I already have Snapshot isolation enabled - I do not have Read Committed Snapshot Isolation enabled - I have been strict with my READCOMMITTEDLOCK hints wherever I truly need them then is there any reason at all to not use the Snapshot isolation level **for all read-only queries?** It seems that all of the costs from Snapshot isolation are paid at the moment that you enable the database-level setting rather than when you run queries under it.