It annoys me even more than no-one seems to care about it much, and most think final is good enough - you can still mutate final objects. In C++ all references are final (in a Java sense) since they can't be reseated, but const actually gets you immutability (modulo const_cast).
I just want everything to be immutable unless mutability is really truly needed!
Otherwise Scala is pretty pragmatic about it (val vs var).
In both cases you still get only shallow immutability, but if nigh every object itself is immutable, shallow immutability may not be so shallow.
Have you tried Rust? It’s nice in this regard; variables are immutable unless explicitly declared mutable.
But it's not terribly easy or even a good idea to switch from Java to Rust at a real company that has no time to rewrite libraries, has to hire developers, and so on.
In C++ you can write a class with some methods that mutate, and some const methods that can't mutate anything, and you can pass around const references through which mutation is guaranteed to be impossible. This all comes for free.
I was thinking that would make it possible to create unmodifiable data objects using that (and not Object as base class).