Why do people play non-latest versions?
If you are new to technical Minecraft you will probably find yourself wondering, why does the machine I saw on Scicraft not work on my [insert latest version] world? The reason itself is really quite simple, Scicraft is not running [insert latest version>, they run 1.12.2.
As well, contrary to popular belief, there are other technical servers, and to top it all off, many of those also run 1.12.x, with some even running more obscure versions including 1.7.2, 1.8.1, 1.13.1, 1.15.2, and more.