If one looks at United's route network versus either Delta's or Northwest's, one can see the absolute need to allow at least two (if not three) connections to complete some of the city pairs which United serves at any time of day. If you carry this farther to specific times of day, then the need for multiple transfers becomes obvious.

As I recall when Delta's route structure included larger presence in LAX, SLC and DFW they also had many city pairs requiring multiple transfers, but with the dilution of their east/west flows they've opted to reduce allowable transfers.

The other interesting factor that comes into play here is O & D revenue management. The only way that these multiple transfer itineraries are available for booking is if they generate what at the time of booking is deemed acceptable revenue not only for the itinerary but also for all of the segments involved.

Bootom line -- multiple transfer generate revenue for United. Otherwise they wouldn't be allowed.