There are lots of these TLDs with restrictive registration policies based on who you are and they tend not to do very well because they're too much hassle and they suffer from a chicken and egg problem; not many people use them so there's little added benefit since the average user isn't aware that they're more restrictive, and then since it doesn't really matter to users potential new registrants don't bother with the increased hassle and cost.
The problem here is that the hassle-free alternatives exist and are open to entities for which another namespace has been designated in the first place.
That's literally what .ltd.uk is for, and no-one cares about it