To be clear: Cohost did take funding from an anonymous angel, and as a result will not be sharing their source code; quoting from your link:

Majority control of the cohost source code will be transferred to the person who funded the majority of our operations, as per the terms of the funding documents we signed with them; Colin and I will retain small stakes so we have some input on what happens to it, at their request.

We are unable to make cohost open source. the source code for cohost was the collateral used for the loan from our funder.

Somebody paid a very small amount of money to get a cleanroom implementation of Tumblr and did not mind that they would have to build a community and then burn it to the ground in the process. It turns out that angels are not better people than VCs.

i used (and use, until the shutdown) cohost as my primary social media site. i'm not surprised, but i can't say it hasn't been disappointing. for all the issues it has (and it did have a lot) it was pretty much the only site that felt somewhat cozy to use for me. stings quite a bit

I'm not shocked.

Their radical idea of building a social network that did not require a either VC funding or large amounts of volunteer labour has come to a disappointing, if not entirely surprising end. Going in without a great idea on how to monetise the thing was probably not the best strategy as it turns out.

I never used Cohost, but I know a couple people who do and fuuuuuuuck this sucks. 'Least Newgrounds is still going, though that's a bit of an apples-to-oranges comparison.