why almost of PTC became a scam

There a a number of reasons really, though it isn't always a case of them becomming a scam. There is a guy who is going around and buying up a bunch of PTC sites, and he does seem to be either a scammer, or a guy who just has no clue how to run a site and runs it in to the ground, either way, he has bought a lot of them, can't remember his name or the sites he owns either.
But there is an inherent flaw with the PTC concept that is very difficult to work around. That wouyld be the adtverising to pay out ratio. In short if you can sell enough ad space consistantly, you are going to end up not having enough comming in to pay your clickers. Most ultimately fail in this way.

Well maybe because PTC Site is easy to create but hard to maintain. Actually there are many PTC script that you can get for free if you search in the internet. But making a PTC site is only the first step. Even if a person who want to create the PTC never intend to make A Scam Site, he/ she end up doing it because he/ she can manage the ptc site.

hey friend....TuiBux is the scam....But Arclicks!!!! Is it scam too???? But in forum i have read many positive responses...tell me guys.??

There are various reasons for the failure of PTC sites. Even if the PTC admins started their business to run then in a legit way, some of the site are forced to go scam as they find difficulties to find the advertisers. The second thing is their investment schemes.
As they have many schemes without much plans, they members are not able to earn from them and they started to file the disputes with the sites via the payment processors. The selling of inactive referrals is the main cause for the failure of the site and in turn, the inactivity of the members is due to the sites decisions, change of terms.

The failure like above are less in number. But the Admins who are starting their business with the plan of shutting down their business within a short period, after collecting the funds from members are more.This is the main cause.

I would suggest you with neobux as they are in the market for so long and they have paid me. I also have rented referrals and most work well in clicking ads daily....

Most ptc sites are scams because people just want to make money off of you. To prevent scammed sites, I suggest checking out reviews of the sites before you sign up for them. Google is your friend.