It is because funding prior to 2010 was drastically less than other areas. There is a need to let those deprived areas catch up.

The most deprived fifth of local authorities receive hourly resources that are 12% higher than areas in the most affluent fifth, after accounting for higher provider costs in London. This results from funding for deprivation, disability and additional language needs in the Early Years National Funding Formula, as well as the Early Years Pupil Premium and the Disability Access Fund.