Yep and old myths die hard.I suspect that it’s a hang over from the now debunked belief that low KH could lead to pH crashes.
The thing is there is a subset of plants that simply won't do well without very low dKH. And to fair there is a VERY small subset that likes a bit more dKH. If you have very high dKH levels there's a pretty big subset that won't do well and your choices are more limited. But as a general rule the lower the dKH the easier it is to keep most plants.