Trend change After 2007

I have noticed that the profit curves of many of the scalping/high performance expert advisors take a downward trend after 2007. Anybody has a logical explanation for this?

I do not think it is because these EA's became known after that date and therefore their performance deteriorated as if this is the reason it should work again after they have been neglected.

Regards,

one of the reason, imo, is when doing backtest, spread is the latest spread got from server, ie, spread at year 2010. and volatilty at year 2007 much less than volatility at year 2010. by using the same spread on a year that has much less volatility, trading cost become significant.

to see volatility from year 2007 to current date, open daily chart, put ATR(288). 288 = 24 days times 12 months. look ATR value at 01.01.2008, this is the average of daily range from 01.01.2007 to 12.31.2007. compare with ATR at 01.01.2009, which is average of daily range from 01.01.2008 to 12.31.2008.

Thanks sangmane for your input. I will attach curve pictures when my MT4 is free to show what I am talking about.