Because RTRT will become a standard quite soon and RTX makes you future-proof more than anything else right now.
BTW, not 3:
Thinking about upgrading to a ray tracing capable graphics card, but are wondering which games support ray tracing and DLSS? Then we've got the list for you.
www.rockpapershotgun.com
First of all: this makes no sense to begin with. Nvidia GPU can't have AMD RIS. So this point is not about DLSS being better than anything else on the planet. It's about having or not having DLSS on board.
Second: AMD RIS and DLSS are doing something very different.
In more general graphics editing terms, DLSS is like denoising. That's why it works well in tandem with RTX. They lead to more realistic graphics. DLSS implementation should be content-aware and not sharpen areas that aren't meant to be sharp.
Some say that it makes the picture less detailed, because people tend to perceive noise (granularity) as sharpness.
That's connected to how some people prefer smartphone photos over large-sensor camera photos. Because it's noise + sharpening.
AMD RIS is just unsharp masking like you would find in graphics editors. It's added at the end of the pipeline. And it makes the picture more crisp all-round.
The big caveat is that - while straightforward sharpening is fairly light load and can be done using normal GPGPU with little lag (Nvidia and Intel do it as well, obviously) - denoising can be quite complex computationally. That's why Nvidia uses fancy tensor cores in RTX cards.
Basically you've rephrased a popular accusation that RTX and DLSS make games look less sharp and darker.
Which is true.