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).