Robert Comsol wrote:
One of the biggest advantages of TAS was that it was an animated TV series, thus there wasn't any need anymore to "compromise" as they could
have visualized anything
they wanted without considering budget restraints.
Not true -- or at least, not true in this specific instance. Filmation was operating under a very limited animation budget, and on TAS's first season they were on an insanely rushed production schedule. So they had to reuse animation cels constantly, recycling the same stock character poses and movements. Putting a simple forcefield halo cel on top of an existing character cel was cheaper and quicker than drawing a whole new set of cels for each character in a spacesuit.
There's also the matter of visibility. Characters in animation need to be easily distinguishable on sight. Putting them in spacesuits would've made it harder to tell who was who in a long shot. The force field belts let viewers see the characters just as clearly as they could normally.