Even the worst case scenario, which is that Arc is a huge flop, and Intel only earns back a fraction of their investment is still better than cancelling the whole thing, not even having the chance to earn back anything.
Have you ever heard of the Sunken cost fallacy?
If they continue the program, they have to continue to spend en R&D, pay for mask at fabs, pay for the drivers teams to support all those sku, etc.
some of the cost can be shifted to the iGPU but not all. At some point it's not worth it if they don't plan to invest enough to compete.
I think Intel have 2 flaw here.
1). they wanted to become a market leader right away and went big from start and faced many issue upfront. I think they should have try at least to beat AMD iGPU to start with and start small and every gen, get a bit bigger while learning the process and improving the drivers. But intel can't stand to not be the top performer.
2. Intel just grew too fast and hired way too much. It take a lot of time to build a team and get good at doing something and adding too much people complicate things, It's much easier to add 1-2 guy at the time in a well running teams than trippling the teams with news guys from everywhere.
I still think that if intel cancel Arc, that is a mistake for them. They need that to stay relevant in the future.