I'd be interested to know what makes up a "huge target audience"?
Birmingham is now a "minority majority" city. White people, who are the traditional audience for motorsports are now only 49% of the population. The other 51% have never considered speedway as "in their culture". So you can divide "huge" by half.
Demographically, Birmingham is one of the youngest cities around. Speedway's typical fans are now pensioners or approaching pension age. And there aren't that many of them in Birmingham's population any more. Speedway has consistently pandered to the existing (& dying out) older fan base and never really adapted to the younger reality. And that will be its epitaph.
Whilst channel hopping on TV, I stumbled on a sport that seems to be reinventing itself. From totally amatur(ish) beginnings, it now has a premier league, a national team, international fixtures, and apparently it attracts (subject to venue size) and average of 1,500 fans per match, which it bemoans as "under-performing" but which speedway teams would die for. Have you guessed what it is yet? Yeah, women's netball!
https://www.skysports.com/netball/news/30100/12058326/tamsin-greenway-netball-must-understand-its-audience-and-deliver-targeted-engagement
So please don't make any more excuses about how a sport can't turn itself around, It can. Cricket has, Darts has, Snooker has, now Netball has. Speedway CAN, it just WON'T.