I think because pay tv was there in the early days of DTT then it set a precedent especially with boxes and TVs having cam/card slots. Pay channels may not have a connection with Freeview but they still get epg numbers.
They get a logical channel number because that's how DTT has been set up in this country. Personally, I would have put all of the pay channels, Gold, Home, ESPN and the Sky Sports channels up in the 300 range with the other TUTV channels. It's not as if they can be watched on most equipment. Unfortunately, as legacy channels they get to keep their channel numbers, that's the way DMOL have organised the platform. Similarly, shopping channels would possibly be better treated as a different genre and given a new range. Again, they keep their channel numbers as legacy channels.
The EPG itself contains a lot of junk, e.g. the red button services have EPG programme information even though they don't have programmes. The EPG data for every channel on the platform has to be repeated in full on each multiplex. Obviously it gets fairly bulky with all of this non-programme information. Then consider that the stream not only contains full programme details of regional BBC 1 / ITV channels for that transmitter but also for the 4 adjacent regions.
The EPG obviously is a useful function but also occupies a similar amount of space on each multiplex as a couple of radio channels.