Take look at this announcement:
For product releases after Java SE 8, Oracle will designate a release, every three years, as a Long-Term-Support (LTS) release.
This means another LTS (ver. 17) should be 3 years after Java 11, so in September 2021. Java 14, however, was released in March 2020, so no LTS.
Java 8 is LTS, but it is not a part of 3-year release cycle, which was announced long after the release of java 8.