I wonder how much of that was a result of the Taylor Report, that, among other things, got rid of the standing room areas (known as “The Kop” in some stadiums).
That definitely had an effect, but I think it’s fairly small in comparison with the fact that if teams can fill their stadia most weeks charging £100 a ticket, then they will.
There have been concomitant complaints about the gentrification of football for at least the last 30 years, including dire predictions that if the real fans become priced out completely, there will be no atmosphere for all the viewers at home - but it hasn’t happened yet. I personally do think it’s sad if a diehard supporter isn’t able to afford to follow their team any more, which must have happened to thousands of people. But it’s probably not the biggest issue with the game right now. The real money in the game comes from TV revenue, not stadium revenue.