It's a bummer but does it not go without saying that museums, like any institution, will come to an end at some point? I don't think that makes it a failure.
Well, some people think of museums as timeless - the sort of place we put 2000-year-old roman stuff, 5000 year old egyptian stuff, 200 million year old dinosaur stuff, and so on.
Of course, the practical realities of most museums are a rather different matter; rent and employees have to be paid, and land in tourist-friendly areas is seldom cheap.
I think car and motorcycle museums in particular live on the patronage of people who grew up when cars were symbols of independence and status, instead of a commodity. So the museums have nostalgic power for the customers, and that’s why they go. But that group is now 50+ years old, so I believe the lifespan of those museums is strictly limited.
Depends; I think the state should have a fund to keep museums that aren't solvent around. A museum should never be dependent on capitalism, that is, ticket sales vs costs.