I mean, the article is from the Ukrainian military. I don't think that Ukraine cares much about whether-or-not the US has capacity to defend Taiwan. I think that the Ukrainian military cares a lot about whether there might be some additional, unknown delay in supply to Ukraine due to slowdowns in the production pipeline. Like, they had the EU promise artillery shells by a date, and they got delays and got half that much at the expected date. I'm pretty sure that they had plans predicated on getting that ammunition, had set burn rates, etc. Then there was the fight in Congress in the US over aid supply that caused a delay. I bet that they don't want more of those. If I were gonna guess, they're aiming to look ahead and say "what might become a delay" and then highlight that as soon as possible to people who might iron it out. The guy from the US says "there might be a month or two delay due to obtaining filler", they want that to be minimized and have a cap put on it.

Gunpowder is used in all ammunition. You're probably thinking of black powder, which was used with percussion caps, flintlocks, and matchlock rifles. But commercial ammunition, artillery shells, and even the big guns on naval vessel still use gunpowder.

But yes, you can still load your own ammunition. You generally have to buy the primer (you could make them, but lead styphnate is really dangerous to fuck around with; mercury (III) fulminate is even worse), but you can re-use the bass casings. You can mold your own bullets if you want to, and there are ways of swaging on a brass or copper jacket, but most people buy the projectiles. Then you buy the gunpowder, and combine them to get the desired chamber pressure and muzzle velocity to get the ballistic characteristics you want.

As for the why - Well, the excuse I tell myself is that, generally speaking, the components individually cost less than the complete ammunition will cost at retail. If you load 9mm ammunition, you might save $.01-.02/bullet, which really only matters at higher shooting volumes, but you have much more control over the exact ballistic characteristics. For rifle ammunition, the savings can be pretty significant. IIRC, cost for 6.5CM ammunition starts at about $1.25/bullet, but I can get brass for about $.20/ea, a primer for $.10, and appropriate powder for about $.15, and a Hornady ELD-M 147gr bullet for about $.50 (or a bit less); that saves me a minimum of $.35 each bullet.

(But really? I enjoy it.)

For making your own ammo I think