I'd wager that those shows likely had higher budgets than TAS did.
If I recall correctly, they were produced by Hanna-Barbera, which did have a higher development budget for each show. So any reusable animations were done first, including extra outfits for primary characters, using that budget. Filmation was one to cut such corners, so they could have larger budgets per episode for the things TREK_GOD_1 mentioned.
Emergency+4 was not a Hanna-Barbera production. It was produced by Fred Calvert Productions, which was a very short-lived company (started by a former supplier of animated segments for Sesame Street). Although FCP landed a then hot property in Emergency!, the company was a small unit and not as well budgeted as Filmation, yet this did not stop the then-common practice of cheap model sheets of several character uniforms as a natural part of their reusable animation.
Further, it is pure myth that Filmation was the only studio heavily reusing character animation, as Hanna-Barbera was notorious for this in all--and I do mean all of its 1970s series, easy to see in any random episodes of Josie and the Pussycats / Josie and the Pussycats in Outer Space, Butch Cassidy and the Sundance Kids, Pebbles and Bamm-Bamm, Super-Friends (every version in that decade), The New Scooby-Doo Movies, Jeannie, Wait Till Your Father Gets Home, the Laff-a-lympics, Goober and the Ghost-Chasers, and yes, Sealab: 2020, along with the rest of the series produced in the period.
Again, budget did not stop the creation and use of environmental suits, unless--as mentioned yesterday--there's official documentation explaining that was the reason for creating the TAS belt.