I do agree that League is a downright mess in team fights, but at the same time, it's pretty true for SCII as well; when the armies, regardless of what stage of gameplay they're at, collide, I'm usually pretty lost as to why one is just eating the other or why this match up is a scenario that requires a retreat.
League has put a lot of effort into spectator clarity, with many of the status effects now having pretty clear symbols, the team-fight view with relative "power bars" that just give you a generic look at which side is faring better, and the commentators are usually fairly good at their fight recaps. A completely uninitiated is still going to miss the majority of nuances in matchups, trades, rotations, and all other such meta-game aspects, but Riot has done a pretty decent job of adding a simple interface for seeing what's going on in a match at any given time, and very simple meter for who is ahead in a team fight.
(It's still a mess to figure out sometimes, eve if you played for several years like I did. Sometimes I can't pick out what's happening until the casters walk us through it on the instant replay)
The problem is that SC2 had very long periods of unwatchable metas. Twelve months of pro games consisting of two players building deathballs, having one battle (Where someone gets caught out of position, and loses their entire army in 5 seconds,) and the game ending was awful, as a spectator sport. (That was any Heart of the Swarm match involving Zerg in a nutshell.)
I was like watching a chess game, that, at turn 15, if one side didn't have a clear advantage, getting decided by a coin flip. This may be fun from a player's perspective, but is awful as a spectator sport.
Really, I think what helps League over StarCraft is that it's pretty clear who's winning and who's losing since there's a relatively easy to follow flow across the map. When one team loses their towers, which are clearly denoted, they're probably behind. Further, gold and experience also give a pretty good indication of who's winning and losing. With StarCraft, which I've also never played, but have watched a handful of games, I find it difficult to follow on a macro scale. Certainly, it's easy to see when one battle is won or lost, but then suddenly one player will concede and I'm left wondering why. I think that rapid nature of forfeiting and loss of the game hurts its spectator appeal.
SC2, on the other hand, is much easier to grok as a spectator. It's 1v1, so you know each army is controlled by 1 player, and the capabilities of the units are far more obvious as well, since a lot of them are based on pre-existing science fiction concepts.
League & Dota get far more viewers because the games are far more popular, however, as a spectator sport, they fall short because of their complexity.