Well I would guess it's because with all the new enviromental standards and anti polution measures the power of the search engine has been severely restricted.
Back in the days when engines could be any capacity and as loud and grubby as you like then you could have used a much beefier search engine, with twin exhausts and overhead dipsticks an all an all. But with all these new enviromental standards then that's just no longer possible.
I'm not really up on all this stuff but I'm sure that must be why.
Isn't it Laurie?