The problem is that it's faster to drive than it is to park, take the R Line to connect to the A Line.  Also, residents from The Springs would have to pay a daily fee to park in addition to the cost of taking the train.  Parking at the Pike's Peak offsite lot is $8/day at the airport.

Same with the western side of town.  I can drive to the airport from Golden in about 40 minutes (on a day with normal traffic) vs spending over an hour taking the W Line to the A Line to the airport.  If I bring family members, the cost to drive and park (along with gas) is cheaper and easier than it is to take the train.