There's an old adage - Time to spare, go by air.

It's an unavoidable fact of life that flights will be delayed, in the main part by weather which we cannot control. Pilots are limited by law to a maximum duty time, it's not that they're just unwilling to work overtime.

Specific hours vary but say a limit is 8 hours. A crew commences duty, gets the briefing, flies A-B and return 3 hours each way, and everything is good. But if they get to B, a thunderstorm moves in and closes the airport causing a backlog of traffic they get delayed at B for two hours. If they now fly the return leg they will go over the limit. They may get an exemption to do that but then are required to take the next day off.
There may also be other implications such as the crew for the next mornings flight ending up in the wrong city.

Once upon a time airlines had sufficient reserve crews around the place to be able to call someone in. Now with everybody cutting costs in every way they can there is no leeway. It's cheaper to cut a flight and bump the passengers to later flights which weren't full anyway.