First, I only answered your question of why they’d bother continuing production instead of pocketing the money, not why it’s a scam.
It’s a scam because they started out with a realistic promise, made their money, and then expanded the scope of the project to be something that is not realistic given their choice of engine, and then switched off the originally promised engine to an engine that still won’t really cut it but is “theoretically” capable of handling such promises, just maybe not all at once.
It’s a scam because “technically checking off the boxes regardless of quality” is, in many places, a scam. Many US states have what is called a “Lemon Law” regarding car sales, where a dishonest salesman will sell you a car that will, down the road, develop a lot of problems that they “patched up” using half-assed but dirt cheap methods.
It didn’t start as a scam, or at least I hope not. I bought in thinking I’d have a pretty good game, some time ago. But their current business model of selling concepts faster than they can deliver actual ship models just means either they’ll drastically speed up the production (and likely lose quality) or they’ll never catch up. The promises they sold in the past that, without having switched engines to support (64 bit was required for many of their promises) means they cannot meet every expectation (some people bought in because Cry Engine was promised, but they no longer use it, and those people will have to struggle very hard to get their money back). The way they keep modifying their ToS to cut customer rights and deny refunding money screams shady dealings, if not outright theft.
They could deliver a flawless product tomorrow and, while I’d being surprised and admit that they actually did deliver a quality product. I’d also still never give them a red cent, because their company treats customers like shit.