It's not exactly that they're recently-graduated so much as it is that it's really hard to find people qualified in graphic design or UX within the last decade who don't daily-drive MacOS, so they're not already fluent with Windows' design language, and have to pick it up as they go, and fill in with what they know works on phones and Macs when they don't know the right thing to do. On the other hand, if you only hire people who graduated decades ago, and really know how Windows users use Windows, you run the risk of assigning too much weight to how Windows users used Windows twenty years ago, and missing out on innovations that became popular in the meantime.