I think it's quite bad for the BRF to not send anyone but if they are going to use the "political issues" excuse then so be it. It's quite bad to see no one attend considering the amount of royals who came to the Queen Mother's funeral.
As Majesty Magazine said, out of the 15 working British royals only two had engagements...what were the other 13 doing?
I am not surprised it didn't go unnoticed rominet09 and it will likely be mentioned many times in the future as poor show on the British part.
Okay, well let's actually look at who these people are.
The "15 working British royals" are presumably QEII, the DoE, the PoW, the Duchess of Cornwall, the Duke and Duchess of Cambridge, Prince Harry, the Duke of York, the Earl and Countess of Wessex, the Princess Royal, the Duke and Duchess of Gloucester, the Duke of Kent, and Princess Alexandra.
QEII doesn't typically travel anymore. Even when she did travel, she didn't typically attend funerals outside of her immediate family. Times when she's traveled outside of Britain in the last few years or attended a funeral for a non-family member are the exception.
The DoE is 93. While he is still seen traveling a bit, it's still not a lot. However short the flight to Belgium may have been, it may still have been more than the DoE (or his doctors) felt he was up to at this time.
The PoW had engagements. The Duchess of Cornwall doesn't seem to typically represent the BRF at foreign events without her husband. She also tends to make fewer overseas trips as well.
The Duke of Cambridge had engagements. The Duchess of Cambridge is pregnant and may very well have felt unable to make a second overseas trip in a rather short period of time - she did just get back from the US - while pregnant and without her husband. Neither of them are full time royals.
Prince Harry is also not a full time royal and has a job. We don't know that he was able to get the time off from his military responsibilities on such short notice.
The Duke of York didn't have any engagements on the online CC so he could potentially have gone, but the online CC is rather notorious for not updating everything this year. Likewise with the Earl and Countess of Wessex. The Princess Royal, however, did have an engagement according to the CC.
The Duke and Duchess of Gloucester probably could have attended... but let's be honest, if he had been sent people would still be upset about the so-called snubbing of the BRF. Likewise with the Duke of Kent or Princess Alexandra - both who have been cutting down their engagements in recent years due to their health problems.