There is more to the cost of airing a pilot than just the production cost of the pilot, and this even assumes the network has agreed to assume the cost of that.
There is the cost of lining up advertisers for the commercial breaks during, before, and after the pilot.
There is the displacement of the show(s) that would've otherwise filled the time-slot the pilot occupies.
There is the opportunity cost of the advertisers you might have lined up if you hadn't punted the incumbent for the pilot.
The more pilots you elect to air, the more often you have to make these trade-offs. If there are a sufficient number of incumbents that can be thoughtlessly traded for pilots like this, I'd wonder about the general program management of the network, and how long they've been allowing things to stagnate.
Even if you just sacrificed a week, that is a huge amount of potential revenue to sacrifice for the sake of picking the "right" set of shows.
And, even if all the economics for airing every pilot works out, it still doesn't guarantee much. You are still gathering data based on what people say they might want to watch based on a snapshot. I can't imagine this is going to be particularly predictive of a series's performance. This seems similar to someone taking a vote on whether a movie sequel ought to be produced from an audience who had just seen the original; I can see far more people asking for that many Scary Movie sequels as actually went to see them.