> the British were unable to change them or simply uninterested?

Can be both. At the height of the empire, Britain's population was only 47 million, while India stood at 400 million. It's hard to really change people when they outnumber you 10 times over.

Besides the logistical barrier, the British Empire didn't need to change India, ruling India without changing up its cultures too radically was working out just fine. Why tear down already functioning structures of power when you don't need to? Many parts of India were ruled through local Indian rulers, who aligned themselves with the British Empire (be it for personal enrichment or simply accepting that they had no other alternative). Playing off pre-exisiting animosity also worked out great, it was much easier to rule over diverse people's who had a past history of fighting each other, than it is to rule over a newly unified homogenised culture.