Fox doesnt know how to keep popular sci fi shows alive for more than a couple seasons.

This is a deliberate strategy, not an error on the business end. Younger actors/directors making shorter production runs in an untested medium are cheaper to employ than serial successes. Friends is a great example of this. Early on, the cast was earning in the high five figures for their work. By season seven, they were getting a million dollars an episode each.

Rather than make one enduring long-run sitcom, you produce a dozen different short-run knock-offs. The uncertainty gives your production company leverage and keeps actors from demanding increased salaries season to season. And with the idea of “syndication” dead in the age of streaming, you never end up paying out a ton in residuals for a show (like Firefly) that has a cult following but a weak initial contract.