Lots of FTers are willing to take the risk of booking separate tickets; not so many with only 2.5 hours between flights.
Had you attempted to book the separate tickets under a single PNR? (Not sure if that would make a difference in the case of IROPS with UA; it would with AA.)
Originally Posted by
peoplemover
What about changing to IAH-SFO they have a similar timed flight
The problem with that is that if the OP misses the first leg of his LAX-SFO-SYD ticket, the entire ticket could be voided.