Since no fraud or loss of user funds has been reported, I don't think there's a problem with these platforms announcing their closure.
Competition or legal complexities might be the reason, but new alternatives will inevitably emerge.
If there are no reported fraud and users are able to withdraw there money, then there is indeed no cause for alarm. That is how it ought to be, what is worrisome is when you wake up and you can no longer see or access the site or when they turnoff the withdrawal option, then that is heart breaking. I think the ones that closed that way in the past are on the chase by the authorities, so that is a welcome development.

UPDATE : Unfortunately, there is a problem, withdrawal aren't going smooth even OpenGradient Co-founder is calling out Bitmart saying they can't get their money out because allegedly they are insolvent even though the Bitmart CEO refuse the allegation that they are running away.
The crazy thing about the picture above is, Bitmart is having a token lock program 1 week before the announcement of their cease of operation. Hopefully none of us locked altcoin on their savings campaign program, I'm sure many of us here are smart enough to understand "not your private key not your coin"
For information, anyone out there who got their withdrawal pending, try $100 or less batches of withdrawals.