The move entirely to PC will kill a good portion of the JP population from playing the game, as PC gaming is nowhere near as popular as console and mobile gaming there. By decreasing the population, the risk increases of the game no longer being profitable, and thus them shutting it down completely. However, with the Sony-and-Microsoft-hosted servers shutting down, there is no choice unless they wanted to spend a ton of money making new development tools and writing a new client for a more modern console. There's little point in doing that with how profitable DQX and FFXIV are in comparison.