Because I've done tracking like that for several years, lots of services are still doing it this way and because rel="noopener" or rel="noreferrer" is the way to go if you want to mask the referrer. Even Google recommends to do it that way[0].
If you are not using it for tracking, there is no point in doing it like this after all.
It's about tracking outbound links, not about masking the referrer. As already mentioned, there are standard ways for that.