Java is an enterprise language, I'd bet every bank in the world uses it as a backend (except the newest fintechs). So the "consortium" is very careful when introducing changes. Also, there's this Oracle issue where they
In 2004 with C# 3 you got lambdas (C# itself was born in 1999) to use with linq, however Java had to wait until 2014 to get streams and lambdas. That's a 10 year difference (not even counting that Python had it a few years before, C++ had it in the 90s, Smalltalk had it in the 70s, Scheme had it in the 60s, or was it in the late 50s?).
Now, with C# 3 and in order to support lambdas C# added variable inference, being able to create variables without having to tell them the type. This can be used outside linq as well, so you can have
var value = 3;
and the compiler will infer (at compilation time) that value is an integer. Same way you can say
var value = new Person();
and it will infer value is of type Person. With C# 9 you can also let the compiler infer by context, so you can declare a class and if you do
Person value = new();
which will create a Person object, but which simplifies more complex scenarios like
someMethod(new() { IgnoreWhitespace =true });
which will create the object that someMethod requires as argument, and set the
IgnoreWhitespace property to true. And remember that C# is a strongly-typed, statically linked language just as Java (of course Javascript syntax is much simpler because it's a weakly-typed dynamically linked one).
For 2021 they are thinking about adding value types (you know, structs from C?) and pattern matching for switch expressions, features already existing in Kotlin and C#. For other features they are pretty on pair with C# (records, switch expressions, etc). I think Java got stagnated until C# started getting some steam, and they probably dismissed it as a simple clone until linq arrived. When you see statistics Java is always at the top 3 most used languages but it's not saying too much, as again it's just that way too many companies are supporting legacy applications in Java and are not willing to migrate... it's similar to PHP, it powers 70-80% of the web but just because 95% of the people using PHP use it through Drupal or Wordpress.
When I write code in Java I cringe, there's so much redundancy, so many words that aren't necessary... I did Android for a year in 2018 and when I saw comparisons with Kotlin I wanted to shoot my foot