I believe airline ticket prices are often based seat demand and availability. SFO is United's west coast hub, so it could be that they are routing most trans-pacific flights through there and demand for seats is higher as a result.
Most airlines run giant data analysis operations on schedule (date and time) passenger utilization and anything else they can collect to derive an optimal pricing strategy.
Most fares are updated once per day and these days even intraday is possible. Most everyone uses SABRE, Amadeus and one other as their reservation backends which have various limitations (Spirit is an example that doesn't but it's very rare and theirs sucks). There are also a ton of caches everywhere to speed up the process which affects latency and increases stale pricing. It's sometimes very chaotic as to what everyone will see.
Also keep in mind that A->B and B->A and A->C->B, etc all have a different optimal pricing structure which is why you get so many odd prices. None of the reservation systems can consider every possibility either, they often have to short circuit a search or it would take forever so you can get variations depending on when/where/from what you look for these fares. Dallas to Austin is pretty trivial to search but small airport in Texas to small airport in China is ridiculously complex as there are trillions of combos.
