The UK is small, nowhere is really far enough away from its final location to make it an issue, perhaps if we were talking about Wick you might have a point. There is high-speed rail and dual carriageway to the M2. Planners in other areas of the world would laugh at the thought that Manston is too far from the network to be viable.
LTC is progressing now with the project out for tender and the DCO going in later this year. Work is due to start in 2025 and it is badly needed to reduce pressure on the Dartford crossing.
In terms of building in the north rather than expensive SE. Thanet is far from being an affluent London suburb. It is an area badly in need of investment and jobs and this airport would do wonders for the area.
I get your point about building a freight hub in the midlands or expanding EMA, but building any new runway is something that could take decades of consultations and still never be approved. At Manston, we have a long runway, taxiways, space for freight warehousing and distribution, an adjacent rail line, a local population largely on-side, and large unemployment in the area. When you look at it like that there isn't a better place really. We will likely lose it under another housing estate otherwise.
If private investment has been raised and they want to make a go of it then good on them IMO.