Blood started to be faced out after the Benoit snafu, as well chair shots/weapon shots to the head being banned since they helped play a big factor in the deterioration of Benoit's brain. Blood was completely removed once WWE went PG in 2008-2009 and the reasoning is understandable. Less blood brings in more money through sponsorships than using blood would have.
Despite some people claiming that "PG is killing WWE" the company is still making more and more profit with each passing year.
Personally, I'm not a fan of the liberal use of blood. It doesn't bring anything to modern wrestling. If it has to be used save it for the end of pure blood feuds, two guys hating each other having their final match of the feud/the build up to it. Bleeding for the sake of blood and "blood being cool" is silly and devalues it when it is needed.