The issue is not so much the fan support but how long it would take for an expansion to team to get up and running. It would most likely be 2020 before a team would be ready. That time frame fits for the tv contracts and the new owner would only be out 2 years of shared revenue. The NFL might be working on that for a 2nd team in LA or an expansion team for one or two of the home markets. The same way they did it in Cleveland. They had the stadium proposal ready but the revenues were greater in Baltimore so the team was allowed to move and the NFL guaranteed the owners contribution for the stadium that was paid back from an increase in the expansion fee.
The NFL is too far along for there not to be a team in LA in 2016.