They didn't remember a fleetwide refit operation in the 2250's to give Starfleet an instant jump drive, that someone onboard had to remember from history class, and institute their own version?
Hmm.
The only ship that's using it is Discovery. That's why I said to
King Daniel earlier, let's see if they actually go on to use it on other ships. I don't think they will.
And it's 120 years later. They can't be blamed for not thinking of it. How much do any of us remember from the 1890s if we're not history buffs? And what if the Spore Drive
is banned due to ethical reasons? Starfleet would try to suppress instructions on how to put it together. It wouldn't be on the Federation Database. So the engineers on Equinox (and Voyager, for that matter) would have to figure out how to put it together from scratch.
Equinox had limited resources as it was. Half their crew gone. Probably nowhere near anywhere to put together a spore drive. Constant attack. There are several factors. They probably thought their Slimer Drive was the way to go. If they didn't use Slimer for Warp Jumps, they would've used Slimer to navigate the Spore Drive. But, if they can't put it together, they can't have a Spore Drive.
And the obvious thing that I can't believe no one has mentioned yet: Kurtzman probably wants the Picard Series and
Discovery to be in the same canon. And the Picard Series is a sequel to TNG. They're not going to tell all the Gen Xers flocking to the series "TNG, the series of your childhood, never happened!" They won't do it because they want Gen Xers, Xennials (like me), and Older Millennials to be excited about the series and that the Picard we all grew up with is back. So if DSC is compatible with the Picard Series, it'll have to be compatible with TNG/DS9/VOY.
So the Spore Drive has to be abandoned due to reasons we'll see. As I said, the whole situation with Stamets sold me on how dicey it is. If it doesn't sell other people on what's wrong with it, I understand, but I think something is bound to go horribly, horribly wrong. "Calypso" probably figures into it too. That wasn't some random adventure. Even though it works very effectively as one.