A lot of publishers complained Adsense ecpm dropped over 50%. Can any expert tell the reason? It is impossble every adwords advertisers cut their cost or budget.
It could be due to smart pricing. If you place AdSense ads on multiple sites, check if the sites have varying eCPMs (both before being hit with smart pricing, and after). If so, try removing the ads from the one site with the lowest eCPM. It worked for me. It might work for you.
I think smart pricing is not the reason because a lot of publishers have experienced this problem recently. And my only one site has over 5 years old and never been smart priced before.
I have tried the same technique but my rpm is still down is there any effect regarding niche we are targeting ? and how to improve it ?
It is possible that lots of bot can be found online. That's why the owner of adsense is making a wise move to protect the reputation from users. Of course it affects those who are straight user to earn money.