He already had his money. He got a $100m contract from St. Louis already, it isn't like he hadn't been paid. If he was really only doing PED's for a contract, that mission was accomplished nearly a decade prior to the 10-year contract. It just doesn't really seem to track that he would only do PED's in St. Louis because of Tony LaRussa, then go to LAA and stop immediately.
I'd assume if he was on PED's he'd have continued. It wasn't like the man got fat and lazy, either. Or had a litany of injury issues. Which are two things commonly connected to former PED users who stop. Pujols just...got...slow, and declined. It was a very fast and stunning decline, but they happen sometimes. Weird declines occur. Hell, no one thinks Jason Heyward stopped using PED's or is 5 years older here in Chicago (he was a top-50 hitter in baseball in 2015). He has always worked hard here. He just...hasn't been very good. The issue is that HoF players usually don't see such weird things happen; I think that's what stands out about Pujols. But over enough time, and enough players, etc...it's bound to happen. I think it just...happened. Pujols just..hit a wall.