I think there are a lot of variables here. Considering the point that 'values are low', I'd question relative to what? In a UK context vs larger countires and global, there are fewer potential users of a .uk domain, fewer customers for businesses using them vs a global market and businesses have wider choice of gTLDs.
Are we talking established businesses or new? Established likely have an established web presence (perhaps this was a little different 15 years ago), so why invest in new domains (I'm thinking a business practically looking at short-term budgets rather than long-term ROI / branding)? Given, at least in my experience, that budgets are tighter, cost of debt is higher etc, what incentive do business, new or established, have to spend more on .uk or a
superior domain when they don't have to? And since 'inferior' is subjective (are we talking domain, extension, both?), is a domain inferior if it achieves the same objectives for less money spent?
I don't think 'stockpiling' has helped, but I don't think it's the cause. I've made what I thought were reasonable offers for domains in the past 10-15 years that remain unsold and undeveloped. I am guilty of holding domains that I have not sold or developed. There are seemingly unloved domains I'd like, but have never been able to find out who registered them. But how many domains are actually 'stockpiled'? How many are advertised as for sale? How many 'stockpiled' domains have potential buyers willing and able to make an acceptable offer right now?
Personally, I think the .uk brand is strong but could be stronger. I'd be asking how do we build awareness and trust in .uk amongst the general public vs alternatives, and what real benefits we can use as selling points in 2024 vs alternatives? This view may seem a bit pessimistic, I actually think there have been some good sales in recent years and domains still offer a much larger return than other assets... I've made more on domains than the stock market