I booked a reservation yesterday using a $200 e-cert through united.com. When I go to view the reservation the system is not offering me any opportunity to upgrade to First. Usually I can see miles or $ options for upgrading. It is a two-leg flight with R/RN availability on both legs.

Why am I not seeing upgrade options? Is it because I used an e-cert to bring down the cost? The flight is LGA-IAH-LAX (much cheaper than the ps fare for early August). Granted, I probably won't buy an upgrade as I might get it without "paying," but I'd like to see what the cost might be.