Why such drastic reduction in remuneration for each click in PTC sites?

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When the PTC sites started functioning for the first time in the Internet as a means of earning online by common people like us, they used to pay a high remuneration for each click. With passage of time, some of those sites have gone scam and more and more new sites have emerged in the Internet. What is important to all of us who are members of such sites is that the pay per each click has been drastically reduced by the sites. Can anyone explain the reason behind such drastic reduction in remuneration for each click? Is it so that the financial condition of the PTC sites is at stake and is not so healthy as it was when they emerged for the first time in the Internet marketing due to tough competition among themselves or is it due to joining of so many members that they are availing the opportunity of exploiting those unfortunate members who have joined them for earning an extra-money?