Well, you are on a public forum with enthusiasts that have interests in the same things as you do, some of these guys will never see your car on the road and some of these lurkers may not be upstanding citizens and may have the means to find out where you live by looking at the license # in your pictures and maybe some of these pics are your buddy's cars and he does not want the tag # displayed for all to see.
Plus on these forums someone is always asking the questions like, "Let's see your garage","let's see your tools", "Let's see your Wife", "Let's see your guns", "Let's see your underwear", so I for one can certainly understand why someone does not want everybody and their Mother and criminal Brother knowing "exactly" where they live.
So if you are interested in what someone has for sale send the guy a PM if he does not want his personal information up there for all to see.
Maybe you have never fallen victim to identity theft or had someone search you out and steal off of you personally, but it happens so if they want to express certain safeguards for their stuff, paranoid or not, it is better to be safe than sorry as not everyone on car forums is a nice, upstanding, law abiding citizen.