As posters such as Vasid already touched on, the key here is the Chinese giant, Tencent. You might remember that in Kickstarter update #94, YS Net announced that they would be partnering with Tencent to publish the PC version of Shenmue III in China. This is being done on their platform which is known as WeGame, but Tencent also owns part of Epic Games. Of course they would want Shenmue III to be on that service too; that way they can bring in profits from more regions than just China (which probably won't be a very good market for Shenmue III anyway). My bet is that this Epic Games Store deal was made back when Deep Silver/YS Net partnered with Tencent (announced December 21st, 2018), and they waited all this time before telling us.
My take: YS Net's financial situation probably hasn't been all that great for most or all of the project. Even with publishing deals, they saw the dollar signs when comparing distribution options. Steam takes a huge cut of sales (allegedly ~30%, but never confirmed by Valve) while Epic is offering a much more attractive deal. I understand their goal and I have no doubt that all of the bean counters came up with the same answer, but I'm in awe that they apparently didn't realize what a PR nightmare this would cause. Of course, none of this matters if Tencent was calling the shots, and I would bet that they were.
