It can take months or years to make additions to existing plants, there is an enormous amount of difference between a solved textbook problem and a real problem being solved.
It's very hard to purify noble gasses, as they are almost completely chemically inert, and chemistry needed to make, say, same argon, to form compounds with anything else is something needing very special equipment, and know how.
Welding grade argon is dirt cheap, 99.999% argon is very expensive, and 99.999999% argon is many times as expensive as welding gas.
It's much worse with neon.
I've worked in a specialty welding shop that did laser and electron beam and never saw or heard of neon used for welding. It is beyond prohibitivly expensive. Even helium is awesome for welding but so expensive that we only used it for specialty jobs that were very low volume and high margin and high risk (e.g. prototypes).
Cryogenic distillation of air is a solved problem. There are plenty of plants already in operation all over the globe meaning there only needs to be modification to existing plants to further collect and crack the remaining 0.1% of air. I'm sure this is not hard to do with existing cryoplants.
If we already have the capacity then why are we without Neon production is a good question. Neon isn't in high demand like the easily extracted major components of air: nitrogen (78%), oxygen (21%), and argon (0.9%). Neon is something like 18ppm in air so a lot of energy has to go in to get very little out. So my guess is economics where the existing Ukrainian cryogenic plants have kept their prices low enough to discourage adding this capacity to new/existing plants elsewhere (maybe they get cheap energy, subsidies, etc). Now it might be profitable.