Exactly, TOS looks like it looks due to budget limit an asthetics of 1960's Sci-Fi (another example of it is Forbidden Planet from which Star Trek designers took inspiration.)
Asthetics constantly evolve.
TMP Enterprise is TOTALLY different from TOS one while keeping it's charateristic details and overall shape, bridge consoles, chairs, corriors are also different due not only to bigger budget but to what 1970's looked (McCoy wears 70's clothes!).
Then came TNG and 1980's where it gave standard of how ships look will look like to 2000's (Designers tried to go outside limitations of so called "Ape Brain" - shoutout to Doug Drexler, and create asthetics that will be not connected to any of curent trends.)
Finally came Enterpise and NASA Punk asthetics, more grouned in reality, yet keeping shapes and technology we know from TOS.
Discovery and SNW went direction of Enterprise and evelove it's technology yet keeping a nods from TOS (shape of captain's chair on Enterprise, shuttles, phasers, tricoders etc.)
I don't see problem in explaining why metal box became cardboard, because designers kept same shape, have bigger budget and look into contemporary art styles.
