Why does the north east of England not produce elite quality footballers like they used to?

I would argue, considering the relative smaller population than places like London, it's over represented in football. You need to also remember there will be people from the North East that choose to go to higher quality academies like Man City or Man Utd. So it depends if you count players poached by better academies. Archie Gray, Elliot Anderson, Lewis Miley, Fraser Forster (a year ago), Henderson, Dan Burn, Pickford, Chris Rigg and Longstaff are all regular Premier League players. That's just for Sunderland and Newcastle, Middlesbrough have Tavernier, Djed Spence and Jason Steele. Sure it might not feel like they're on the level of the people you listed but you are taking a timespan of 30 years. Clubs are more globalised now on a whole too, everyone is competing with players not born in the same country never mind region so naturally there's going to feel like the top players aren't from one region when this is the case countrywide. Middlesbrough have a very good academy while being in the Championship which they've built for years. Sunderland give good first team football to their academy players and Newcastle are poaching some of the best talent in the country and world at under 18s level.