Actually I agree ... I use the decimalisation all the time myself in my own punting - it makes mental calculations a lot quicker(!) However, the traditional way of displaying odds is still being perpetuated by the bookies - particularly in the shops and also in the media (which I have to base my writing standards to). Also most punters still seem to prefer the odds written that way!
I think it is gradually changing to decimalisation, and the "new" odds are helping to drive that .... for example you never used to get 9/5, 11/5, 12/5 in the past ... and you rarely see 85/40 or 8/15 any more .... plus the fact that most online sites do offer fractions or decimals will help expedite things (default is still fractions though).
One of the layers at Plumpton last year had the horse I wanted to back at 15/4, I had to use the calculator on my phone to work out it was better than the 7/2 generally available before lumping on. I prefer fractions but only the more traditional ones.