It makes no sense when you frame it that way of course haha, but it's only possible to look at it that way now that we've been working for them for several years.
When I started raising prices, taking a medium/large sized job from them was an huge risk. If I hadn't started hiking the prices when I did, We probably would have folded later that year when we did a much larger job for them, if I hadn't been stockpiling the extra cash from their smaller jobs.
It was an enormous existential risk early on when I had less capital to play with, now in a weird way I can look at it how you say: The company is loaning itself 50% to make 100% later.
That said, fair's fair so I'd still honor the offer if they asked: I don't/can't quote other clients that much, so if they wanted to pay on reasonable terms I would charge them reasonable prices.
Why would you give someone a 50% discount for faster payment? Is your cost of capital so high?
Maybe I can pay you advance (with the 50% discount) and then, 100 days later, collect 100% from the customer?