If the UK was still relevant in the world, the BBC would continue to fund this.

Utterly vapid comment. I'm not even going to bother "defending"the UK but if you like you can ask an LLM: "What do you think is the most important/relevant international city in the world?"

Anyway, on the actual material of your comment, It's got nothing to do with the BBC choosing to abandon longwave, it's because the technology is completely out of date and obsolete.

There just aren't people making the equipment/infrastructure anymore. The BBC already bought up literally the entire global supply of the valves they need back in 2011, and that was only 10 valves[1]

[1] https://www.theguardian.com/media/2011/oct/09/bbc-radio4-lon...