Because people like braces (they provide structure) and there is a risk to break backward compatibility.
Granted the whole ;} = 5; syntax is not great ....
That must be why they removed the need for braces with 'lambda' methods right?
It just seems so pointless and ugly, no one is going to write them like this (well, seems unlikely anyway):
public int X
{
get;
} = 5;
So they're no longer providing a scope/block structure. How would it break backward compatibility? I'm not suggesting they remove the scoping for properties, it's clearly needed for {get;set;}, but as far as I can tell I can't think of any existing property-name suffix keyword in the C# grammar, so it seems it wouldn't be too hard to get it to work.
The only reason I can think of to not do it is to reserve the option of post property-name keywords for future features.
I've been using public readonly fields instead for a number of years now because of the constant boilerplate. I doubt I'll change to use these auto-properties for the same reasons.
