The plugin allows us to create our own custom knock back mechanics. Includes a lot of features.
https://www.spigotmc.org/resources/randomkb.48891/
Skript exists, yes, but not everyone knows how vectors work + I've tried custom kb with Skript, and it just didn't work.
Yes, Skript exists, but it would be a lot more complicate and would require more time to make instead of just having this plugin. Mind you that the plugin has tons of knockback mechanics, like combo mode etc. Also, shrugging off every plugin request with "Skript exists..." is a topic we discussed before.