Why isn't it standard included in FTB Packs, anyone that comes on here and asks, "How do I improve my FPS?" And the first thing everyone says is, "Add Optifine."
So why isn't it just like in there by default like FTB Utils is.
Okay... this topic again. Right, let's do this.
First off, the developers of Optifine have an 'all rights reserved, do NOT redistribute without permission, and that includes modpacks, which you do NOT have permission to include'. They aren't on Curseforge either, they have their own website, so unlike most mods, they haven't accepted Curseforge's ToC which includes right to redistribute. So there is an actual legal issue involved with including it in modpacks, because they have asked people not to. FTB Utils, on the other hand, is 'you are free to include in mod packs so long as credit is given and you aren't making money off of it', like most mods on Curseforge these days.
Second off, Optifine is not the end-all-be-all you seem to think it is, and in some cases it can actually make things worse. It depends on what sort of system you are running, really. I'd rather use something like Fastcraft than Optifine unless I was going for HQ texture packs or shaderpacks.
Third off, historically, there have been many issues with Optifine and how some mods render things, especially back in the 1.5 and 1.6 eras. Even in 1.7 era, there were some mods that had issues. I haven't been using Optifine lately, so I can't speak to its compatibility lately. However, if a mod does custom rendering, there's at least a solid chance that it can cause... issues. Ranging from simply rendering improperly to outright crashing because of conflicting resource grabbing.
Optifine is only really useful to people with already high-end systems who are wanting to make things look nicer using HQ texture packs or shader packs. If you are just trying to get it to chug along at 30 FPS, Optifine is almost certainly NOT going to help this happen.