Your plain and simple obfuscates things.
Not all elements of ic2-exp are bad. Not all elements of IC2 were good.
Oh no, I am not saying that IC2 was the best mod ever with no fault, and IC2-exp is the spawn of satan.
However, what I am saying is IC2 had nothing inherently wrong with it, just that it was losing popularity as it was reluctant in its move in unification (will talk about this later). And I personally feel everything added in each iteration of IC2 exp made it worse and worse.
I thoroughly enjoyed Gregtech as an addon for IC2, in 1.4. It overhauled IC2's difficulty, but didn't mess with any other mods (which is why I don't like the newer versions). However, even in the early days of IC2-exp (which really needs to be IC3, as it is nothing like IC2 was) I could see it leaning more towards the difficulty levels of Gregtech over the original IC2. Now, I know it is nowhere near as hard as GT, even back in 1.4 when GT wasn't too hard compared to today's releases, however its difficulty and tedium levels are a lot higher than IC2 ever was, or I ever wished it would go.
As for the unification. As of 1.6 it was obvious that IC2 was only being kept alive via modpacks that force its usage, and people who actually like the mod more than the RF equivalents. The problem with IC2 was, as soon as RF started to rise to power, that EU wasn't compatible. Buildcraft/Railcraft/Forestry all took a hit to popularity as they used MJ, but were still widely used due to MJ being compatible with RF, meaning people could power all of their machines, apart from IC2 (when looking at the "big mods"; not mods that were generally excluded from packs such as Reika's mods) from their RF generators. Not to mention RF generators were plentiful. IC2 was quite limiting in how you could produce your power, whereas RF could be water or wind, sun or heat, and as 1.6 became more stable (about 1 year before FTB released unstable for 1.7) you could even have reactors, potions, PINK STUFF, and more powering your generators. So even if IC2 had the better machines, which from a user point of view, the only good one was the induction furnace - and equivalent with the IC2 addons, as they were faster than the RF equivalents.
Then we come to 1.7, EnderIO and even Thermal Expansion both big players in the RF field, had ways to make all of your machines faster if you were willing to put in the effort to upgrade your machines (with EnderIO being the easier, and obvious choice, for most people), it meant that not even the high speed machines were exclusive to EU any more.
And the kicker for IC2 which means it is showing its age, and reluctance to make itself popular is the cables. As a lot of people already mentioned, they LIKED the fact that the cables blew up (or fizzled away would be better), etc. And they removed that, but they didn't thing to add in facades or multipart support. As someone who doesn't give a damn about looks, this wouldn't sway me, however there are people who make amazing builds, and covering cables is a necessity, and you can't really do that with IC2 without having a 3 thick wall (or having panels which look off).
Oh, and for the people who say there's no alternative to the drill in an RF mod, the draconic evolution huge pickaxe thingy works just like that, but works with wood and mobs too? (I dunno, I don't use DE).
The biggest issue with IC2, in terms of being a popular mod, is it doesn't cater to what the average user wants - less resources needed to use the mod, less time/effort for the user, easier than alternatives. And IC2 is going in the opposite direction; it takes more time and effort than ever before, it uses more resources with no apparent reason why, and it is a lot harder than any of the RF alternatives.
However, I understand there are people who like hard, and/or just like IC2, however, I feel it should go the way of Fz and stop being included in main FTB packs, as it isn't used by many people unless it is being forced unwantedly (such as in infinity: expert mode)