FiveThirtyEight was never a fit at ESPN, and wasn't at the NYTimes either. The difference now is that ESPN is stressed, and that's the bigger factor.
Cable/satellite TV, which ESPN is propping up through bundling, is also fracturing and moving to subscription/ad-free models. ESPN might be the last to go that route, and when it does other Disney properties will probably have done the same—and the biggest loser, long-term, will be sports talent, which have been overpaid downstream by brand advertising to captive cable/satellite viewers (which include those watching on other screens using their cable/satellite logins).
When the whole mess becomes pay-per-service and/or pay-per-view, we'll have a whole new market with greatly flattened costs and incomes on the supply side.
We've already passed peak subscription. ESPN will surely be among the winners in the new game of musical chairs for who wins viewers' time and money, because appetites for sports won't go away; but how ESPN wins will be the main question in the meantime.
As for FiveThirtyEight, I always thought it made the most sense as a standalone entity. If it had stayed that way and grown on its own, it might by now have become an alpha brand that owned other brands. Instead it's a depreciated asset for sale by a stressed owner. Kinda sad, but not surprising.