For some, it's a matter of preference. But there are good arguments for it - the viewfinder isn't limited by display resolution, for example. On the other hand, modern mirrorless cameras are marvellous, too. For example, the camera can bring your attention to areas that exceed the camera's dynamic range (and would thus be too bright / too dark), or highlight exactly which bits are in focus.

So the digital versions are getting better, but there are still reasons to use an analogue viewfinder. It's not as clear-cut as you think. I encourage you to try it out!