From the article @pinkybrain posted above, for ease and to explain:
Why have they been actually allowed in for the past 28 years?
The answer lies in the very different media landscape which existed in 1989.
Sports departments of national newspapers and their news desks operated very independently of each other.
Independently and often competitively.
…
Mike Ellis, The S*n’s Merseyside based sports reporter at the time, was as appalled as everybody else by his newsdesk’s decision - and that was recognised by the football club.
When the likeable and enormously respected Ellis retired in 2003, the UK Press Gazette reported: “Ellis was on the brink of leaving The S*n in the wake of its coverage of the Hillsborough disaster that created uproar on Merseyside, but was persuaded to stay on by Liverpool FC’s then chief executive, Peter Robinson.”
They then quoted Ellis.
“I was so upset over the way it was handled that I wanted to quit, but Liverpool talked me out of it,” he said. “They said, ‘It’s not your fault, why make yourself a martyr’. “Despite the coverage, the club never withdrew their full co-operation although if they had it would have been understandable. I’m just glad I didn’t quit.”
Phil Thomas took over from Ellis and inherited the goodwill and respect he had generated.
But since the Hillsborough Inquest finally and belatedly delivered a verdict of unlawful killing last year - delivering the first signs of justice at long last - people have demanded accountability.