Vanilla servers are a terrible reason. Vanilla+Forge+FoamFix will still consume significantly more RAM and CPU power than vanilla alone, or even vanilla plus LiteLoader.

When the 1.8.9 version was released, it was already missing a lot of contemporary fixes and features - this is because it was a quick release specifically created for low-end computer users to enjoy Thaumcraft 5 and Intangible, two content mods which will not likely make it post-1.8. That's it.

Out of scope. Sorry.

"Should" and "need" are unwarranted here - I think "can" and "want" are more truthful.

Again, this is out of scope - I have no time to maintain the 1.8 version. Sorry.