I'm sorry but I have to say this.
The reason that there has been so little coverage of foreign royals at today's ceremony is that the vast majority of British people don't know that other countries even have royal families. The weddings of the Swedish, Danish, Norwegian etc couples received next to no media attention in the UK, except for in Hello magazine perhaps which only a very small proportion of the population would read.
So, why would the BBC spend time talking about people the British population, on the whole, neither recognise nor care about?
I mean no disrespect to any of the foreign royals but this is just the reality of the situation.