Because with a 2 year vocational degree, your basing your worth based only on your vocational skills. The unquantifiable benefits (your results may vary) of college include but are not limited to: a) collaboration with others b) social engagement c) research d) conflict resolution, etc. Sure you get these skills in high school and you can get them anywhere else. However, the fact that you got into a 4 year college (and I'm talking about any top 50 ranked colleges, pick your list) provides a somewhat coarse but useful aptitude assessment as to your abilities.
I associate the difference between having your work done in the US or outsourcing it to India. Sure, they have coders there and some are really damn good. But somehow things just don't turn out the same/as well as something programmed by the people I hire here (and pay an arm and a leg for). They can do the grunt work great but wow have you seen some of the interfaces or design logic they produce?