My guess is that if she could deicde herself bot King Albert II. and Grand Duke Henri had paidm StateVisits to the UK a long time ago. But it is the british Goverment whon decides who gets invited and it seems they have no Interest for State Visits from this 2 countries.
But that is strange. Why then have State Visits from the Netherlands? With all due respect to our Dutch posters, I can't see that the Netherlands would be more important to the UK than Belgium.
1