Originally Posted by
jonsail
I am wondering if the "failure" to offer a single intinenary could be that one portion is a code share with another airline and the other portion on UA and UA doesn't want to pick up liability for a misconnect that is the fault of the codeshare airline??
No, that has nothing to do with it.
There's no failure.
emcampbe's explanation is quite good. Airfare is not sold on a point-to-point basis; it's sold based upon origin and destination city. The connection points, 99.9%+ of the time, are irrelevant from a pricing perspective.
If the MGA-LAX fare were combinable with the LAX-LAS fare, you could get the price you want. However, most international fares aren't combinable with most domestic fares, because they treat MGA-LAS and MGA-LAX as independent markets.