Because its an older body and the article authors wouldnt make affiliate income from the links.

Any RF mount camera will give you great results but you will be locked into a relatively new and expensive lens system with fewer options for third party lenses. A cropped sensor can be good for wildlife but will also restrict what lenses you can use. I’d recommend something like a 6D which gives you the benefits of full frame sensor and can use EF mount glass without an adaptor.

When you say nature photography are you thinking of landscapes or wildlife or both?