They explicitly said they would charge if it was the same license on a different machine. Originally they would even keep charging if it was your original machine, but backtracked on that. Still, how do they determine your original machine? It's likely that some replacement, perhaps like a motherboard, would trigger it. Obviously a full upgrade would cause them to pay again. But yeah, if you have something like Steam Deck and a travel laptop along with your PC... that's three charges to the devs.
They could easily do a single fee per sale but for some reason they want this tangled mess. It almost certainly is meant to target FTP games. I don't know why they couldn't have just given a different pay model for just the FTP games.