That's true of some effects, but in TNG the core spaceship / space station models were shot on film, and then composited with other effects like phaser shots.

In DS9 / Voyager as I understand it, they transitioned from using models to directly generating the whole shot with CGI at NTSC resolution. See https://memory-alpha.fandom.com/wiki/CGI#Acceptance

This means that in TNG they just had to recomposite the film with a newly created high-res phaser shot; whereas for DS9/Voyager they would have to recreate the whole shot in high-res CGI.