This is basically the main reason for photo ID check. So the airlines simply ask everyone to identify theselves as it would be too time consuming to only check the ones that have bags checked in.

Outside Schengen is a different matter. As someone posted, airlines receive hefty fines if passengers arrive without valid travel documents. I was denied boarding last year to Moscow because my visa wasn't valid until the next day.
Agent told me that they would get a fine of I think 3 or 4000 USD and I'd be sent back on first flight.