Here is my understanding of openHAB2 history.
When OH2 started there were some companies interested in using OH in their products. Our developers started Eclipse Smart Home as the OH2 technology base, hoping to attract company participation, OH2 became the free implementation of ESH with some additions.
One company donated the developer resources to develop the Paper UI. It was not completed before the developer abandoned it and they used a technology not familiar with our other developers. OH developers began looking toward other UI options for OH3 and recommended the Paper UI for administration use only.
After several years (2+ I believe) of not getting any company participation, it was decided in January 2019, after 2.5M1 had been released, to merge ESH into OH. 2.5M2 arrived 8 months after M1 with that merge and a completely redesigned build system. That is why 2.5 Stable was no released in the normal 6 month cycle.
Although OH3 has been declared as the next major release, there is also work on a patch release 2.5.1.
Here is the ESH intrgratuon annoincement,