I can see where this line of questioning is going but what's the connection between Britain and Chagos or the US and Chagos for that matter?
The United States of America has had sovereignty of itself for 248 years, should the USA give up it's sovereignty in North America or do you draw the line between somewhere between 215 and 248?
At what point do you say, it is what it is?
When you've lost the argument.
Indeed, I would like to understand the answer to the above question better, since the only reason I can see is that Mauritius as a colony used to govern the islands, and that seems to have just been a convenience of the French that doesn't strongly justify any current claims of sovereignty. And since the UK were the ones to forcibly evict the Chagossians from the islands, it seems a double-injustice to "return" their land to another sovereign power which is equally at a distance from the islands themselves. Do the Chagossians support this claim by the Mauritian government?
They've complained about not being part to the discussion, but in practice most of them have Mauritian citizenship now, and it should be easier for them to deal with the Mauritian government to reclaim some of their land. It's a lesser-evil situation.