Well aide from the whole possibly not having either of his starting Tackles on the field, there are many other reasons he's not getting the love.
1) You mentioned how much better he'd be if he cut back on INTs, you're right. Fact is, he hasn't done that yet, so his value is dropped because he throws about 1 INT per TD. In fantasy terms, that means you're usually getting 2 less points per TD, instead of 1 less point (good QBs should have closer to a 2:1 ratio).
2) The running game. Its great to have a stellar running game for a QB because it relieves a lot of pressure and opens up the passing game. Well, not many people are counting on 16 games from Faulk, and Jackson while he has a lot of hype around him, is an unproven rookie. In short, the Rams offense is going to have to rely on the pass moreso than before, and defenses should be able to key on it because of that.