A technical limitation itself is insufficient, but a
lot of art is on purpose limited in order to force focus on certain things.
E.g. black and white photography is often used to emphasise composition and lighting more. Specific palettes. Specific sets of instruments - a classical composition will not usually be for "some random number and set of musicians" but written for or arranged for, say, a quartet or a symphony orchestra. Both visual art and music tends to follow a whole range of rules to match certain styles.
And yes, reducing size is also a choice - the demo scene takes that very seriously for a good reason: it again forces a different focus. A non-size constrained demo category emphasizes cooperation and teams working on different parts, and project management and is a totally different thing than, say, a 4K demo where you have to focus on reducing a single concept to its essence.
A direct size constraint may not be that important for most games (though for some it is: people still develop cartridge games for the Commodore 64 for example), but resolution and palette constraints do act as implicit size constraints too to a great extent.
Well done pixel art is just a form of minimalism in art that focuses on shading and composition and exploiting patterns and how we interpret pictures. Just reducing resolution of a picture almost always produces bad pixel art. E.g. r/pixelart on Reddit includes this rule:
Art must be comprised mostly of pixel art using pixel-level manipulation.
Color reductions, index painting, computer generated, oekaki, aliased
digital painting etc. are not permitted unless they have been cleaned up
by hand afterwards or were posted with the [WIP] tag.
And people there get very picky about this, to the point that some people object to even fairly basic paint application tools (I've argued with people who claimed that a pixel based "spray" tool is not suitable for pixel art, for example, because there's not sufficient thought behind each pixel placement; I don't agree with that, but I do agree with the overall idea that you need to pay attention on a pixel level, and tweak things that does not look right). Taking e.g. a photography and color reducing it and reducing the resolution does not result in good pixel art - it results in pictures that are messy and unclear and that often lose a lot more detail vs. a proper pixel art rendition of the same scene.
Similarly reduced palettes forces much more conscious thinking about composition to make it make sense.
Modern pixel art, like modern chip tunes of course have different motivations from "authentic" art made because the constraints were real constraints of the hardware, but it's really no different from people who e.g. choose to compose for piano even though they could compose for a synth and be free to include sounds no piano can reproduce. We have not entirely abandoned piano music just because we now have more flexible instruments available.