The reasons for the lack of commercial success of UK hip hop are legion:
1. Westwood not supporting it meaningfully (his business relationship with Universal Records coloured the playlist) . Steve Lamacq may have supported it equally well.
2. Bad business (Low Life Records) / unprofessionalism
3. Big Beat music (Fat Boy Slim etc) pushed by majors (aka Instrumental Hip Hop)
Many of the prominent UKHH guys have been semi-retired for Ages. Many platforms require people to pay to be featured (e.g. GRM) so that's why you won't see them.
i mean Big Beat was't just so much "instrumental hip hop" as it was beefed up hardcore made in mind to try and get alt rock listeners to get into electronic music but not THAT much of a leap away from what was familiar to them. so lets keep it a buck its not like say just UK hip hop was affected
Westwood i know that coloured it but also considering how the UK has always tended to rep East Coast as far as taste goes its like why would i settle for a weaker version even if its homegrown compared to the guy who can get all the exclusive tracks,appearances and freestyles from them. Grime was when he started backing UK music but like again as you said it was more a gesture.
Steve Lamaq might have been a good shout too but he's more a indie rock guy than anything and that connection ties into what i've said before about backpack rap and people not willing to engage with rap on its own standards.
Somebody like Young Spray who these days is more a podcaster than a rapper even though he came up through rap with Northstar because he was in and around people who did grime and Northstar were heavy on the roads AND he was able to manage the leap to road rap and follow current production trends he's been able to keep in the loop likewise with Blade Brown seeing as he's got that album with K-Trap out recently.