Why don't the Dukes of Albany and Cumberland claim their Dukedoms?

In 1917, King George V of the UK stripped the Duke of Albany and the Duke of Cumberland of their dukedoms because these 2 members of the extended British Royal Family lived in Germany and supported Germany during WW1 against Britain. However their heirs, also members of the extended British Royal Family and in the Line of Succession to the British throne, are free to request that the dukedoms be restored. The Duke of Albany would be Hubertus Prinz von Sachsen-Coburg und Gotha (German Duke of Saxe-Coburg-Gotha) and the Duke of Cumberland would be Ernst August V, Prince of Hanover, Duke of Brunswick. Ernst happens to be the current husband of Princess Caroline of Monaco. (Since Caroline is Catholic, Ernst is no longer in the Line of Succession to the UK throne, but his children by his previous wife are). So what gives? It's been almost 100 years since WW1 and since these dukedoms are still being held in reserve for these guys restoration shouldn't be a problem. In fact their respective fathers and grandfathers could have asked for restoration. It's not like they don't play by British Royalty rules, Ernst even asked Queen Elizabeth's permission to marry Caroline