Why would it? Crosstown West going to the airport is a substitute option, not a complement. It is slower but cheaper rapid transit option between downtown and Pearson.
My understanding is that it was not The Crossways being NIMBY, it was asking too much. Metrolinx futureproofed their tunnel under the tracks, but told The Crossways to go fly a kite until they came back with a more reasonable price. Frankly, I don't know why Metrolinx does not pursue some kind of expropriation.
It stays, unfortunately. And that's been the UPX's problem from the beginning; it's not enough of an express train between Union and Pearson. Making a UPX stop at Mt Dennis is not helping much; while a 15 min UPX ride for ~$5.40 ($4.85 Presto) vs. 27 min Crosstown ride for ~$3.25 ($3.00 Presto) seems like it would be an attractive option (especially thanks to TTC fare hikes), it adds time to the total trip between Union and Pearson, which hurts the key segment of UPX ridership.