Introducing our first auto-generated chart – WordPress Versions Lifespan. Historical chart displaying lifespan (in days) for each major WordPress version. Source
Version lifespan is the difference (in days) between two major WordPress versions. In other words, how long did it take to release the next major version. The data is based on release dates of all the major WordPress versions.
For the first couple of years WordPress had no official release schedule. With the release of WordPress 2.1 in January 2017, it was decided to adopt a regular release schedule every 3-4 months (90-120 days).
According to the chart, for a short period of time the goal was achieved (2.1 – 2.6), then for a long period of time they exceeded this goal (2.7 – 3.7), and in recent versions the core team managed to achieve this goal again (3.8 – 4.6). A third of all the major versions exceeded this goal. WordPress 4.7 had a longer lifespan and seems like WordPress 4.8 will have a long lifespan too.
The chart by itself does not explain the trends, it only shows historical information reflected from the data. Technical analysis alone does not mean anything without a context.