I would. For one, his BABIP was probably affected by a combination of slight decreases in LD%, HR/FB and GB% with an increase in IFFB%. Also, one bad year of BABIP is a fluke, several is usually a trend, like almost everything else in baseball. Your BABIP tends to be low if you don't make consistent hard contact and are slow as molasses.
But he didn't do it. And even if he had hit 30, it would still have been the worst full season of his career. The 30 homers isn't the point, that's just the straw you're grasping at.
An increase in BABIP by itself does little, unless it's large and sustained. And it's unlikely given Teixeira's statistical profile anyway.
Beltre played in Seattle, and he's long been a suspected steroid user. Crawford was coming back from injury and (surprise) is injured again. Lackey's pitched 45 IP, Wells is not a good example, since he had an on-off good year bad year thing going on a la Beckett.
You did not provide a single example of what i asked. You're talking like this is something that doesn't happen all the time with baseball players. They decline. Sometimes abruptly. This seems to be the case with Teixeira. Maybe he has some nagging injuries, maybe the whole switch hitting thing has taken a toll on his abilities, who knows? But the numbers don't lie.