I actually love it internally - the wood panelling, vaulted ceilings and corner fireplace are very retro now rather than dated. The bones are great and with a sensitive redecoration and lots of mid century modern furniture it would look fabulous.
I don’t know the area at all so I can’t speak for the price but you say it’s not overpriced for the area so clearly that isn’t an issue.
I would imagine it hasn’t sold because the layout isn’t going to work for most people. It’s got an annexe and a bedroom that’s only accessible via a separate entrance. For a small family with an older teen and elderly parents it’s going to tick all their boxes, but for a family with young kids needing the 5 bedrooms the listing claims it has, it’s not going to work at all and is going to require building work to turn it into a property that works as a single family home.
As such it’s a property that will only suit/appeal to a small sub set of people. I don’t think it’s necessarily that there are nightmare owners. It’s a property that’s very much of its time that has been designed for the needs of a specific family set up. If you don’t like the architecture/design of the 70s/80s, you’ll hate it, and if you don’t have their specific family set up, you’ll need to spend a fortune on integrating the annexe into the main house.
If I wanted to live in your area OP and had the cash to do it up, I’d buy it. It’s big, airy, unique and distinctive. I’d have a field day decorating it!