Re: That's horrible.
Probably for the same reason that my brain went "car engine?" when I saw "1.8L" - Average Joe doesn't know about niche equipment - they'll recognise a Mac, or a smartphone, but won't have a clue about the value of a camera lens.
That and most people are inherently good most of the time. Compound that with wanting to just get out of there, and the fact that the owner could literally be the guy next to them, people are generally going to not going to just pick things up.
I came across a notebook the other day - leather bound and clearly full of content - bound to keep it shut - while shopping. I ended up leaving it where it was, in case the owner came back for it, realising where it was. I did flag a member of staff as I left though, so they were aware.
Who knows what value any secrets in it could have held?