Getting a request approved is a nightmare. It's literally easier to get a search warrant from the courts than it is persuading police SPOCs to approve your RIPA request.
The gatekeeping is fearsome. They take their duties incredibly seriously.
But The Guardian reported in 2014 that "EE, Vodafone and Three give police mobile call records at click of a mouse", and in 2015 that "UK police requests to access phone calls or emails are granted 93% of the time", with rejection rates varying wildly by county from as high as 28% to as low as 0.1%. So it doesn't seem to be as hard as you're making out, unless things have changed wildly in the last few years. May I ask your sources?
https://www.theguardian.com/world/2014/oct/10/automatic-poli...
https://www.theguardian.com/world/2015/jun/01/police-request...
The filtering isn't about civil liberties (although keeping councils out seems sensible) but rate limiting requests via paperwork, so only important ones get done.
Incidentally, the ability to perform unrestricted arbitrary queries without a warrant across the entire phone-location dataset is a fairly horrifying amount of power for the police to have. But I suppose legally that ship has sailed with RIPA, and now it's just a question of the fine details of the implementation.