I didn't find any great statistics, but according to this fan forum post and redoing the math a bit for your question, 277/355 squeeze plays where the bunt was laid down lead to a run scoring - about 1/3 of them with no outs recorded (so either the bunter is really fast, the pitcher/catcher mishandles, or the throw is to the plate). Another 49 of them were probably safety squeezes - ie, the runner on 3rd doesn't just run all out, but takes a big lead - so really 277/306 were successful, or some smaller amount of successes with same 29 failures (as some safety squeezes were also successful).
So, yes, the squeeze play is nearly always successful once the bunt is laid down. It's not all that successful overall - it raises the Win Expectancy when correctly done, but not by a huge amount in most cases - but that's not really part of this question.
In terms of 'what the pitcher was thinking', part of it was probably that it is indeed hard to throw someone out on a squeeze. Unless it's a safety squeeze, they guy is halfway down the line when the ball is bunted. Think about it in terms of throwing out a guy stealing second - that's hard, right? This is harder, because you have to pick up the ball and throw it from a worse position, AND the bunt takes a while anyway. It's also relying on the catcher's positioning and your accurate throw, all of which are hard for a pitcher who's probably not all that practiced on defense. It's also hard if he was a righty as he has to turn around to make the throw. Not every pitcher is Mark Buehrle.
Part of it is also, keep out of a big inning. Guy on 3rd one out, for example, sure, you allow a run - but you prevent 2 or 3 if you don't get him out. The run expectancy for 'guy on 3rd, one out' is 0.97; so getting the out and allowing the run to score is sort of 'default', a conservative play but not necessarily wrong.
Finally, you don't say who it is, but it's spring training. Is this a guy with a 80 on his back? The really good players might try to make the play, but they also might not be all that interested in stretching for a spring training out. The guys with 80s on their backs (ie, the guys who are trying to impress the major league staff but don't likely have jobs right now) are going to make the conservative play if they're smart, because it makes them look mature, like they understand how the game is played, and aren't overeager young'uns who try to make every out like it's the bottom of the 9th in the World Series.
Now, if it's actually in the 9th, tie game, in the playoffs, you can bet your life that he's throwing home...
