"Hi Mr Berman, can we use the Borg for the 40th time this year, and I want to write the 15th time travel episode for this season, and would you mind tripling the budget so that I can invent a completely new CGI species. Thanks, Mr Berman, you're a doll."
Enterprise saved money in it's last season by doing two, three and four part stories, so that they could hire the guest stars in bulk, and reuse the sets, and sfx several times, rather than trying to build 20 different alien worlds in 20 episodes... So why on earth does Star Trek rely mostly on a 40 minute play?
OH!
The budget for Seska and Cullah and their Kazon shit, was folded into the SFX budget (for ships and explosions) in season 3 moving forward, rather than continuing to pay for more speaking parts on the show to spice the story with recurring villains or lower decks fun.