I guess GPS jamming was not routine for them. Had they been aware of any NOTAM regarding GPS interference, they'd be prepared, and, like you said, would have VOR setup prior to leaving the ground.

If you area a pilot and can't handle GPS dropping out, or the failure of any other single navigation aid, you should not be flying.

Checking NOTAMs is important.

Systems fail for all kinds of reasons, if you're dependent on one SPOF without any backup, bad things will happen eventually. In aviation we're taught to think this way from the very beginning. Always have a spot picked out where you will attempt to land the airplane when (not if!) you lose your engine.

Even in the absence of GPS jamming, you can effectively lose GPS for all kinds of reasons in a plane--a connector failing somewhere on the back of your panel, a wire chafing through, etc. GPS is nice, but it's probably a lot less reliable in most light aircraft than the other options.

It's been 20yr since I've flown a plane, so maybe attitudes have changed, but my instructors always stressed the importance of always being able to fall back quickly and seamlessly to a paper chart, your watch, flight computer, and basic instruments. Because you will lose everything else at some point.