I reckon the number of sales of the game was pretty irrelevant to them. They lived off investor money for years, and the fact that they released something makes it rather difficult for them to be sued for fraud. I suspect that's why they never took pre-orders, too - it makes it more difficult for any "false advertisement" class action suits to get any traction if they weren't accepting any money.

Here's something that isn't that widely known outside of developers/publishers: Steam holds any money from the sales of a game until the end of the following month - it makes refunds easier, it gives them time to deal with processing fees, etc. So The Day Before's devs, who said they had to shut the studio because they'd run out of money and couldn't afford to stay open because the game hadn't sold well enough, wouldn't have seen any money from the game until next week anyway. And they'd have known this - this wasn't their first game.

Based on how many titles in the past have pulled off the "launch in Early Access, grab a lot of money in the early hype, disappear" strategy, I have to imagine something like that was the intention.
They probably assumed that there would be a big enough pool of naive fools that would believe in the game for just long enough to get away with launching a below minimum viable product and cashing out once the reasonable refund window was surpassed. And, considering that they were the best performer in Steam for a hot minute, you can't blame them for thinking that.
They just overestimated how much they could get away. Which, considering how much some other titles have gotten away with in the past, is saying a lot.