If the choice would be a mutable one, making it expressly immutable after the fact serves no purpose. As it is, the compiler gets to choose an efficient list for the data provided, and then refuse to compromise on that efficiency later. You might as well use an enum. What useful collection implementation would require immutability? Even arrays are more flexible.

Sure, it's nice syntax, but I can come up with more scenarios where I'll want to initialize a collection than scenarios where I want to finalize one (well, excepting for the fact that this is java, where immutability is often considered a virtue).