Blackpool North has ticket barriers so it can not be revenue related. I too have always been baffled by this one. We have dozens of other similar seaside town terminus stations and they allow anyone to freely walk on to the platforms. It makes it a very unpleasant station to visit. Blackpool South is nicer to use.
I work at Blackpool North, there's a number of reasons why pax aren't able to go onto the platforms till the train is ready and most of it is Network Rail won't spend the money on infrastructure.
Only two of the six platforms are covered and even then only a quarter of the platform is covered from the elements.
No help points,No yellow lines,No benches,No signage such as timetables etc,No destination boards on the platforms,No CCTV that can monitor all the platforms and there length, all of these are requirements stated by RSSB for a major terminus for passenger platform waiting use,Compare BPN to Liverpool lime street.
Also BPN is self dispatch by the conductor.
Also the trains are cleaned when they arrive and 195s and 331s can have there toilets tanked at BPN without the worry of passenger interference.
Hope this helps.