If there is a market for the downloads, the government shouldn’t need to get involved. Maybe the production companies are unaware of the potential viewers willing to pay to download these programmes. Might be worth contacting them and if you get a positive response posting links on the forum.
Unfortunately it still comes down to money at the end of the day. To be able to offer downloads a production company would need to buy the rights to be able to do that for each individual production (and costs can vary hugely for different productions) before making it available.
So that requires a huge outlay with no guarantee of covering the costs - something that many production companies just aren’t in the position to consider even when they are aware of potential paying viewers.
This is exactly the sort of thing that needs government assistance. Welsh culture includes Welsh TV, and we wouldn’t and don’t blink twice about government assistance for museums, library, books, or for the Eisteddfod. Why should Welsh TV not be supported to widen access to their cultural outputs?