I'd say the root cause is a basic unwillingness on the part of some people to respect certain mod authors' basic requests. They're not asking for people's firstborn.
Let's try hitting at this from another angle: You want to use BluePower4 in your mod pack, which I made. I demand that everyone that wants to use it is required to get permission from me before using it, as well as include a link to a specific page that has pictures of puppies on it. You include the link in your pack, and ask me for permission as you are working on getting together the rest of your pack. I, though, am off on vacation on Ares, and won't be back for a few months. What do you do?
If you use my mod, you are not respecting my wishes.
If you don't use my mod, then you don't get to use the content you want to use, and your users suffer.
If you use my mod, ask my permission, and make sure to tell me that you're going to use it until I say otherwise, you might offend me because I am a delicate flower and have to remove it later.
While my example may seem overly silly, it really isn't all that silly as we get posts with people asking how to deal with this issue all of the time.
Currently, if you want a custom modpack, the end user is the one that suffers as they need to compile all of the mods, put together the configs in a way that allows them to function together, test to make sure your items and blocks don't overlap, and then stress test to make sure nothing else conflicts strangely. And, of course, there is constant updates required because there WILL be conflicts that you miss.
Instead, what if it was as easy to make a custom modpack as it is to use one of the premade packs from FTB? What if you just picked out mods from a list, and then waited as your launcher built that pack, and then launched it. You'd still end up with some troubleshooting in the game as there would still be mod conflicts, but given a good system people would be able to submit the issues directly to the launcher, which would then go to the mod authors. Unified technical support? Yes please.
The biggest bottleneck in the modded MineCraft community is the keyboard to chair buffer on the enduser's end, as most people that play modded MineCraft don't have the technical ability to deal with the vast majority of issues that spring up. If we can fix that, everyone will win.
I'm not talking about private modpacks or whatever, I'm talking about how much effort it takes for the people maintaining the packs. Right now, the FTB team has a huge slog to keep all the mods and configs up to date in all their packs; this has been mentioned to me a few times by the people involved. If FTB is in any way based on the Spout or Technic launchers, there are complicated YAML files which (in my experience using YAML... I tried using them for MPS keybinds and recipes but) are very easy to permanently damage just by having the wrong indentation style set in your editor.
YAML are just ugly files with horrible formatting, having used them via Bukkit for long enough to know that people CAN use other systems (tabs, commas, non-declarative spacing? What joy is this I feel in my heart?).
That aside, though, does the Technic Platform really help in regards to the config files? From what I've seen, all it does is allow you to declare new versions to your modpack, which people then download automatically when their version is older. It then overwrites the more recent version. If that is the case, it won't end up being all that much easier for the FTB team, unless I am mistaken in regards to what you meant (or something else. It wouldn't be the first time, nor the last time).
Now, if the Technic Platform was designed to allow you to upload only the CHANGED files (for example, everything in our pack stays the same, but we update MPS to version ∞.3.4 (from ∞.3.1), all we'd need to include in the modPack.zip for the latest version would be (besides the folder structure of course) the updated MPS version. If it worked like that (or works, I am not sure. If it does, please tell me so I can do a dance'o'joy) things would be a lot easier in regards to the amount of data that'd be constantly flying around.
Meanwhile, the private server I play on has switched over to Platform and we get fresh mod updates every day,sometimes more often if there's a bug in my MPS release or something.
Excellent, I am glad to hear that it is working properly! The server I'm co-running will likely be switching fairly soon as well for that same reason. An example of a recent problem: Someone accidentally murderboated the server because we were using an older version of ExtraBees. We updated the version of ExtraBees, and everyone had to manually update their version of ExtraBees. This wouldn't be that much easier in regards to time (we'd still have to spin off the new version of the modpack to our pack repository, and people would still have to download it) but it'd be that much easier in regards to effort ("Where do I get that mod from?" "Where does it go?" "Who are you, again, and why are you on my computer‽" could be heard. Our userbase is fairly good in regards to these things, though) is vast.
A better example: We decided to upgrade to XyCraft's latest version fairly late at night. We all manually update our XyCraft version, only to find that it requires the latest Forge version. In MultiMC, this is fairly easy to resolve, but it's still something that most users have not done. Everyone got through, although the headache of having to deal with this manually is fairly up there. And trying to imagine a userbase of non-technically savvy people really gives pull towards the Technic Platform.