Op literally says why....to make it easier to sell 🙄
Nobody has suggested they couldn't decorate it however they wanted while they were living there
Of course they can.
But most people do NOT have a Disney mural home. Therefore most people would probably not want to BUY a Disney mural home. Therefore it would attract more people and be easier to sell if the home was decorated in a neutral manner. None of this is rocket science.
Yes someone else might love it and be willing to pay as is - but the chances of someone looking in that location for that price at that time who would love a Disney mural home is far lower than the amount of people looking in that price and location and time for a home they can easily decorate themselves/has minimal work needed. It's not like just one coat of paint will be enough to cover up the black outlines in the hallway or the maleficent room - in most of them the whole ceilings and walls will need about four or five white coats before any colour on top of other work that needs doing - the kitchen looks pretty old etc.
If you have 2 otherwise similar houses and one you can move into straight away and the other will need lots of work 99.99% of people will pick the easy one.
If they are not bothered about a quick sale and want to live in their house the way they like it until it is sold - which as it says "no chain" might be the case - then fair enough, which is why OPs heading wasn't "aibu to think people shouldn't be allowed to decorate their houses however they want."
You're arguing against a point that nobody has made.