Allow me to shed a little light on this topic, from the perspective of a fan site owner.
Fan sites are hard. The combined amount of work it takes to build and maintain a great site that people would like is more than you might imagine. Humans like being acknowledged for their efforts, too; and when people think of the fandom's creators, musicians, artists, and writers come to mind, but fan site operators are generally taken for granted.
Like most fandom activities, running websites is not a particularly profitable endeavour. There are exceptions (two that I'm aware of) to this, but most of the world's pony sites are completely and entirely volunteer-driven. If a site owner, for whatever reason, loses the motivation to continue pouring hundreds of hours of their lives into their site(s), they're fully within their rights to walk away from it - just as a musician who loses the motivation to make more music can just walk away from producing any more. Depending on the level of attachment to the work, there may be an emotional battle that needs to be fought, but really... site operators have no obligation whatsoever to continue their work in the fandom from day to day.
If there are any sites you cherish and want to continue existing, do their staff a favour and say thanks. Let them know you care, that you appreciate their work, and throw in a personal note of how the site has positively contributed to your own life. A simple gesture like that can make a world of difference to us.
And please, do not fall prey to bystander effect - do not assume that "everyone else is doing this," and that such a message would be a pointless waste of your time. You may be surprised how human website staff really are.
Traffic doesn't just "come". Just like site operators don't owe the community their work, the community doesn't owe site operators their attention. But, it is a two-way road, and when a site operator has done everything in their power to get their work out there, no one cares for it, and they're not getting anything else (such as a salary) for their efforts, can you really blame them for wanting to move on with their lives?
As has already been said, Hasbro has nothing to do with this. The C&D's they've sent out were always sent out for the exact same reason: someone was publishing a project that they held a trademark to (Hasbro does have trademarks for MLP animated entertainment and video games), was polished and faithful enough to pass for official Hasbro material, and was incredibly popular, too. The point at which a cursory glance at a project does not immediately reveal whether it is fan-made or official is the point at which Hasbro seems to take concern, judging by their past takedowns.
I'm not sure what you meant with this - what are you comparing private website ownership to?