The reason these sites don't do it more aggressively up front is simple, the users fall off. Each step there's a probability they exit so reducing the steps increases their net conversion. However, faceted searches, by which the customer is looking at granular features, trims, odometer limits etc. convert to leads and sales higher than non faceted. Basically a pretty linear relationship between facet depth and conversion.
This effort, to get people to facet while keeping them from leaving is the whole ball game, and has been the pursuit of all the smartest people working on this problem at these companies for the last 25 years. It would need a really strong up front message that educates them on it an makes it super easy / intuitive.
I think the sites have come a long way actually. They've integrated payments into their sites which has made a big improvement for the customer and if you look you can see how available they are taking the initial make + model+ zip search and letting the customize their search after.
@joe.pistell can chime more, as this is his area of expertise.