It wasn't ignored by the rest of the press. Private eye was one of many outlets, an important one granted, but the story was repeatedly reported on and investigated over the years by the local papers, Computer Weekly, TheRegister, the BBC, ITV, The Guardian, etc. Indeed Nick Wallis, an independent journalist, has covered it very closely for a very long time (including a special in an issue of PE):
https://www.postofficescandal.uk/
The scandal has hit the headlines many, many times across all the outlets, particularly in 2019-21 with the litigation and appeal cases. It was the subject of an episode of BBC Panorama in 2015 (fronted by Nick Wallis).
But it all comes to nought. The victims are still out of pocket and still have criminal prosecutions. If the media are to blame, then so is the judiciary, and so is the government, who have had it in their power to provide financial redress. And of course the Post Office and Fujitsu are the culprits.