Maybe the costs are cheaper and it would be easier to buy an exchange than start and market another one from scratch. Poloniex is still a known exchange that have loyal users in spite of the bad service.
I reckon Circle does not want to be become directly an altcoin exchange. They need Poloniex to be that for them.
I can only assume they know more about this type of thing than any of us ever will, because from the outside it looks totally batty.
400 million dollars buys a lot of skills, marketing and staff to be applied wherever and however you wish. It's undeniable that Poloniex was racking up huge numbers once upon a time. Perhaps the deal was put into motion while it was still huge.
Then again internet-related VC spending has a long track record of laying out vast sums just when users clear off for good. Myspace is now a ghost town. Friendreunited made the founders rich and then vanished. Crypto is possibly even more fickle.
Time will tell I suppose and people like this might have some major vision even if it's unappetising to us lot. Or they're fucking clueless. Stuff like 21.co burning $100 million to sell a few hundred tarted up Raspberry Pi's would not have impressed me if I'd funded them.
There's a book to be written about the VC world because I certainly don't understand most of it.
