That's not really fair though. Tons of people apply for jobs because they need a job. I've surely done it in the past. I've applied and accepted jobs I didn't give a damn crap about. I had to pay rent, feed 2 kids, and pay my wife's tuition. And even did so with multiple jobs at the same time. Anything else was secondary. I went into interviews, praised the greatness of the ideas of some shitty startups which were doomed to fail. I always showed up prepared and was "professional" (in so far as you can show up and not give a rat's ass, but not let it show), and always tried to show I was invested by having already ideas about their products, website, etc... But still, didn't actually care for that stuff.
So, I was motivated and a good "employee", but was I a good fit? Probably not.
And, on the other hand, I also actually did interview at times just for giggles. Or for practice. Or just in case. Or to get leverage.
And when I was the recruiting, while I surely wouldn't assume that the person in front of me would be "interviewing for giggles" (at first), I can totally understand the "weren't sure if I wanted to work there". Like I answered on another part of this thread: the onus / burden of proof is on you, you are the one who has to show you really want to be there (even though you actually may not).
It's screwed up, but it's how it is, because we also work for money. I know I did often. Still did my best in any job I got though.
(And you should not expect that either, actually. I'm similarly pissed by friends or colleagues who tell me "damn it's like these guys don't care about the job or don't give it all". Well, heck yeah, why would they?)