That's just it, though - other species can't enjoy advanced tech, either.
That is, none of these specific one-off technologies has been made the galactic standard, by the UFP or by anybody else. If the Sikarian teleporter isn't available to all in the late 24th century, why would it be that at any other timepoint? There would always be greedy Federations around trying to grab this sort of stuff. They all have failed with the Sikarians, so the Federation should, too.
Timo Saloniemi
And this highlights where DISCO gets contradictory, not in a minor point, but in the very basic plot point for this season. Did The Burn affect just the Federation, the whole Quadrant, or the whole galaxy? The focus is just on the Federation almost to the point the rest of the galaxy doesn't exist. Klingons used dilithium and had dilithium mines. Unless dilithium is somehow exclusive only to the Alpha and Beta Quadrants, there should still be plenty of dilithium in the galaxy.
There were plenty of major powers outside of the Federation that had FTL drive systems. We keep mentioning the Romulans, but the major objection is the collapse of their empire. I just said Klingons. We also have Cardassians (they were major enough to hold a vast territory). Kazon had a lot of ships (but maybe they were all assimilated). Hirogen, Krenim. Borg. Dominion. None of these are small 1 planet civilizations. Are they all suffering? If not, then why haven't they been able to give/trade/sell stable, working FTL systems or dilithium to the Alpha Quadrant? It's been 150 years. Plenty of time to get back on one's feet, especially if there are friends or friendly folks willing to help.
Then there are the smaller civilizations like the Ferengi, Breen, Children of Tamar, Talarians, all the one-shot aliens of the week, Again, plenty of civilizations to turn to to sell/trade/gift either dilithium or alternate FTL tech.
As for teh Sikarian teleportation system... yes, maybe they were all assimilated. The Federation and/or the Romulans have had access to a working Sikarian teleporter since PIC. That's 800 years time to study and replicate that piece of technology, especially with the data Voyager acquired.
Yes, we see that warp and dilithium are still being used, but the supplies are running out. They've had time to switch over to an alternate fuel (yes, I know dilithium is not a fuel) source.