I wouldn't say our area is rich but it has some big old houses on smart streets that sell well, lots of parks, is at the seaside, and countryside, excellent schools, good for small town/large village shops. There are some less expensive bits and certainly not everyone is very comfortably off but there is a sense of a community and of it feels safe. We look after it- lots of community groups set up to do so. It gets tourists, has attractions.
But about 4-5 miles away is a much poorer and run-down small town (some beautiful old buildings) with a 'sink' area (the south and west of the town) that has been like that for at least 40 + years. I wouldn't live in that 'sink' area if it had the nicest house ever in it (it has no nice housing). It's crime-ridden, has every effect of ingrained, long-term poverty, low-achieving schools, is dirty and poorly looked after, really run-down streets, high levels of addiction, high unemployment, poor health statistics, high social services input, lots of anti-social behaviour, the metro station is regularly subject to police 'operations', the area is worrying to walk around. The local council throw money at it but economic and social forces keep it in the state it is. An old area of the town centre has been restored- lovely buildings, Georgian houses - it felt like they stood a chance of balancing the scales a bit and attracting some more wealthy people in which would have a knock on effect on money spent locally- but whilst that was happening the Tory government arrived and hacked council budgets, the pandemic hit and the effects on the economy mean the town centre has barely a reasonable shop left (there's a small ADSA and the rest are poor stuff- Heron's, charity shops, vape shop) and is mostly empty and boarded up.
The people who live in the the lovely old houses (and there are those in the north and east of the town) don't use the town centre- they shop and socialise in other small places in driving distance. The 'sink' bit is increasingly isolated by poverty. People investing won't take risks with money there because of what it is and has been.
I don't know how you change that.