Why did SFO move UA Flights to Terminal 1

Flights to LAS, SNA, and SAN on United Airlines operate out of Terminal 1 at San Francisco instead of Terminal 3 where united does other operations. Why did United want to expand to Terminal 1? I mean i know this used to be were flights on Continental used to operate. I think it is inconvenient that people need to transfer terminals to get to their destination. Im not unhappy or anything, but my question is, why did United decide to relocate operations for flights bound to Orange County, Las Vegas, and San Diego?

Those flights were moved because it’s a lower percentage of connections than many of their other flights and those 3 destinations have enough flights to occupy the gates all day long.

They expanded into Terminal 1 because their space in T3 was full and CO already held the leases to the space in T1.

i don’t get what you mean by “lower percentage of connections”. Does it mean more people fly to those destinations nonstop?