Airfare is only cost-effective if it's either a) one person, or b) time critical. Otherwise, car travel is much more feasible.
As for your blurb about truck traffic, think again. It's also 93 miles shorter. At $2.60 a gallon for 6mpg works out to $40.30 PLUS the I-35 toll. That's why trucks don't take I-70 to I-135 to I-35.
Even if not a freeway, for all the work Colorado just did on US-287, there is limited abilities to pass from Limon to the Oklahoma state line. Namely in Hugo, Kit Carson, Lamar, and the few truck lanes on hills. As for VPD, drive the road sometime and tell me it doesn't bottleneck horribly. Especially when some trucks hit their governor at 60-62mph. That's fun being behind them with no chance to pass.
The biggest problem is not that it isn't a freeway. But a lack of passing opportunities, no bypasses of small towns with absurdly low speed-trap set speed limits, and a general direct route for people. Besides, google's routing algorithm doesn't factor in actual drive times, but estimated average rates given a road's designation. So of course it see's I-70 to I-135 to I-35 as the best, although I've timed it legally and can do US-287 faster, given that I can pass slow vehicles when I need to, and that's even with all the lights from Lamar, Dumas, Childress, and down through Decatur.
But, be snide. That's fine. Be reactive instead of proactive. Wait until there's a problem instead of seeing it advance and making sure it doesn't become one.
Sykotyk