It is not uncommon that these monuments to riches are abandoned. The huge fortunes needed to sustain them are broken up among family members as the cost to maintain them spirals and the number of really skilled artisans decreases.

I remember reading about a much larger mansion in Long Island that was offered as a donation to the government because the family could not maintain it; the government couldn't either. There is a website that lists historic homes for sale and you see all sorts of stories like this (though only a few homes of that magnificence). One such home was a Czech castle outside Prague, but that seemed to be in pretty good shape.

To sum up, the loss of beautiful estates is not always the result of neglect or avarice; sometimes it's simple impossibility.