FFI makes cross-platform usage more questionable (have a look at python or node breaking a build on windows vs linux, this is very very rare in case of Java builds), and Java is more than fast enough for most use cases that it simply doesn’t need FFI for speed (like Python for example).
Also, this is a huge advantage of the system, you don’t shallowly depend on a ton of C libraries, you can be confident that your whole application to the last bit is properly abstracted (plus can be debugged and observed with the same great tooling).
Eh, Java leaves quite a lot of performance on the table compared to C or Fortran. It's not as bad as Python, but if you really want to go fast, it's not quite able to compete with fine tuned native code. The Vector API might help a bit, but I don't think it will go all the way.
We'll see how far value objects and the vector API go. The lack of operator overloading makes writing scientific/numerical code a bit awkward, though this could be mitigated by using Kotlin instead.
Also, this is a huge advantage of the system, you don’t shallowly depend on a ton of C libraries, you can be confident that your whole application to the last bit is properly abstracted (plus can be debugged and observed with the same great tooling).