Spore drive? Where was that in TNG?
There's nothing primitive about any of the Starfleet or Klingon technology. Klingons have cloaking devices for a start but Enterprise already jumped that shark years ago so it's not just Discovery to blame.
The spore drive was incapable of being mass-produced. You need a tardigrade or another sentient being with tardigrade DNA to run it (like Stamets). And since the tardigrade in DSC teleported onto the Glenn because of the activity in the mycelial network their s-drive experiments were causing (the creature was drawn to this), and is potentially a sentient lifeform, it would not make that same error/decision again.
So the spore drive is a one-time freak thing that only works because the tardigrade was present, and because now one person has the DNA to make it work, although at potentially great risk to himself.
So, without needing to be handheld through TEH CANON reasons for why we never see it again, I actually think that the answer is pretty evident already.
And no one else in 100 years ever attempted it again? Not even the Klingons, who are well aware of its existence and would gleefully use it to their advantage?
Where are the Klingons going to get a tardigrade?