Why index on low selectivity column hurts query performance
Access to a row using a non-clustered index, which idx_name is, requires extra random I/O: b-tree lookup finds the clustered (primary key) index value, then you need to go and fetch the actual row from the clustered index.
The alternative is a sequential scan of the clustered index itself, which does not incur that extra I/O cost and is also simply more efficient by being sequential, not random.