I'll have a go.
Because there are no adequate mechanisms for collecting/reporting the figures which would produce meaningful national statistics - something which Professor Jay highlighted in interviews. The table from the CEOPs report has to be understood in that context. It was the result of a six month investigation set up after the Rochdale localised grooming case in 2010 which put this issue onto the agenda.
The whole report
is here and the executive summary
is here.
Quoting from the latter :
It defines 'localised grooming' :
(It's perhaps worth emphasizing that the Jay report deals with all forms of Child Sexual Exploitation not just 'localised grooming' although the latter has for obvious reasons attracted the most attention).
The report then explains - at length - how limited the data it had to work with is.
CEOPs report :
(...)
(...)
In short it makes abundantly clear that Police forces and other agencies had generally not identified this as an issue and did not keep records about it. These figures are likely - as the CEOPs report makes clear - to be skewed by the fact that the areas which do keep any kind of records are those where the recent street grooming trials have taken place.
I'm - to say the least - unimpressed that these 'statistics' are being quoted to win an argument about race without making clear how severely limited they are, arguably to the point of being meaningless, except as a starting point for further work. A more blunt way of expressing that springs to mind.