In the past with Java 8 JFR wasn't free for use in commercial production environments. So we built our own profilers. It's nice that with NFTC, Oracle allows you to use JFR in production from Java 11 onwards. But they can revoke NFTC anytime. So, it is still wise to develop and use open-source or private alternatives to JFR. Besides JFR still doesn't profile everything well and you still need to build infrastructure for integrated distributed profiling and tracing.