CBS and NBC desperately need to build a prime time game show line-up like ABC has.
Actually they don't. They have their own summer strategies, and have done decently enough with their respective approaches. CBS can still count on Big Brother to be a reliable performer in the key demo, chewing up nice chunks of the schedule. Their summer original programming has fared less well of late, but they also have a stock of procedurals that can deliver decent enough results on a second...or third....go around.
America's Got Talent likewise chugs along at NBC, while American Ninja Warrior is a utility player they can lean on.
Just because ABC found a niche, for a couple of nights on the schedule, doesn't mean it is necessary nor advisable, for the competition to follow suit.
And as for Fox, they had Beat Shazam, though I have not read one way or another that I can recall about a third season. They also had Love Connection...however you want to classify it. On the radar, they have Mental Samurai coming up...so they are not devoid of games.