If the UK was still relevant in the world, the BBC would continue to fund this.
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comment, It's got nothing to do with the BBC choosing to abandon longwave, it's because the technology is completely out of date and obsolete.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...