Mobile Suit Gundam

You know how in Star Trek whenever the ship took damage consoles would explode?

Well in Gundam Seed whenever the ship takes damage the Captain MILF shows off space jiggle physics.

That's my theory on its enduring popularity

(Also the fight with the Desert Tiger or whatever they called was pretty cool iirc)

I think a lot of the mech designs are pretty good in their own right as well and that's ultimately what keeps a Gundam series relevant, model sales.