Squash have a tendency to take over…everything. They go every which way if not trained properly, and training them can be a chore. Those heavy plants can destroy standard garden netting in nothing flat, and they don’t always appreciate the upward growth requirements.
A squash arch allows them to grow somewhat horizontally, with enough real estate that they don’t get tempted to go off every which way. And, if they do, it’s easy enough to return them to where they should be.
Check out this tutorial on how to make one from PVC and wire fencing.