That happens when you miss a FG and have phantom penalties and no-calls go against you.
And the OL without McCoy is simply not the same.
And it's not uncommon for teams to come out flat in the first half. At least the defense played alright in the first half.
Second half was all about adjustments. The Rams made them, and the Saints offense wasn't able to finish even though they managed to tie the game in the 4th. They were driving late and I think it's possible the outcome is different with Taysom in there at the end.
That said, the Rams' offense is absolutely loaded and I'm surprised the game was that close.