Apple's philosophy around high pixel density is to be able to run at a scale factor of 2. (Or close to 2 on mid-2010s Apple laptops, or sometimes 3, as on newer iPhones.) That way everything is physically the same size, but looks a lot nicer. Mac users running 5k monitors aren't running 5120 x 2880, they're running 2560 x 1440 at 2x.

> ... is that with bad eye sight due to aging things get blurry anyway

Until they get so blurry that reading glasses are obligatory. And then, suddenly, everything is sharp again and that hi-dpi is nice :)

Totally agree!

> One problem with high pixel density is that you either have to scale everything up

The bad news is, as a Windows user, very few apps support scaling (aka DPI awareness).

For larger displays, ex: 49" with 5120x1440, you'll take full advantage of every pixel without scaling.

Sure, but I'm using a 5k2k 40" display. I had to wait ages for it to come out, and it's hardly "retina" quality, but I can't imagine having a significantly taller 49" display with 3/4 of the lines.