I'd say you are right on some points; doing realistic artwork with Illustrator requires a lot of skills. Not only the designer needs to know the software very well but also needs a powerful computer and real artistic skills to translate vectors into high quality illustrations. The illustrator needs to have a perfect control of the paths, blending, different gradients and know how to draw. It's really a mastery of the software and art, it's normal you won't see a lot of these artists.
I know people who do amazing illustrations in vectors that are amazingly realistic and complex. But they also have skills (and patience) that honestly I cannot even hope to achieve myself even though I work with Illustrator for almost 20 years. So to answer your question, yes I do think it's a matter of skills, practice, patience and preference. If vector could be compared to physical kind of art, I guess it's close to engraving and sculpting. The more small details you'll add at small scale, the more realistic you can make you illustration.
On the other hand, Photoshop is very close to real life painting and is maybe easier to use for some kind of digital art. I guess it's easier to develop techniques, create montages, merge pictures, add lightning and all sort of effects that are not always easy to achieve with Illustrator; I think it's easier to be a "hack" with Photoshop. I also think it's easier to do some trial-and-error and get good results.
You will need to try and see if you're more a vector type of digital
artist or a digital painter. You can combine techniques as well, use tablets, buy brushes and presets, etc. Some designers here feel more comfortable with Photoshop, others with Illustrator, and in both case hey all develop more skills and mastery in one or the other. Some in both, with time and practice.
Why choose one more than the other? Being an expert at vector design is a very unique skill that few people really possess. You could be hired to illustrate encyclopedias, medical books, packaging, and all sort of artworks that need a super sharp output at any size. Digital art made with Photoshop is more limited in how it can be used because there's always the resolution factor that also affects the file size and final result; once a digital image has been done at X resolution with Photoshop, it cannot be increased much, while a vector can be used at any size. So becoming an expert illustrator with vector can lead you to very exclusive projects that few designers can do.
The 2 images you posted will probably be easier to achieve in Photoshop... But I'm more a Photoshop person, some vector experts might be able to recreate these vaporous effects and ambiance with vectors. I don't think it's impossible but it depends why you would want to achieve this in vectors too; it's a lot of work.
Here are some examples of very high quality vectors: