why? google and facebook are a distribution channel for people search. just google the name of you mother, grandmother, father in law, anyone not in the nerd, hacker, geeks segment and show what turns up (note: on the resulting pages, turn off your ad-block)
in non US countries the business model is mostly ads (from the sh*tload of pageviews), in the US the business model is mostly affiliate (delivering traffic to the thousands premium "criminal record / financial record background check" companies)
People don't always use their legal name on facebook and not everyone has enough online presence to show up on google. Peoplesearch pulls data from many sources e.g. your electric/water/broadband company.
huge market and growing (growing with every new person which gets online, with every new person which gets into employment ready age)
dominated by a few big players, just waiting for smaller niche players.
the only downside is, that you get about 5 "i will sue you" emails per day if you reach a certain size (just ignore them,....)
said that: www.facesaerch.com is for sale