I didn't mean to suggest they're just in it as a cash-cow (because buying a football team that's been stuck in the fifth tier of English football for an eternity is a terrible investment if your aim is making money).
They've both got a clear affection for the club and the local area, but the fact remains that they aren't going to hang around forever just because of that, and especially if it starts costing them money they aren't prepared to invest.
They're riding a Disney+ wave at the moment, but the documentary will have a shelf-life (especially if the club linger around League One and League Two for a while, which is very possible), and as I understand it, it's the documentary money that's doing a lot of the heavy lifting with the current investments into the stadium, squad, etc.
It's probably going to make for reasonably compelling viewing even if they miss out on promotion this year, but if they miss out again next year, or spend multiple years mid-table in League One after being promoted, it's going to be hard to make that an entertaining watch to anyone but the most invested viewers.
From what I've read, they've probably got enough to make a go of League One without additional investment, but even that's likely to be a big step up from what they've been used to in the National League and League Two and be a multi-season project to go up from. The Championship is a whole different ball game, let alone a push for the Premier League (or premiere league as the yanks like calling it).