I have played starcraft for ten years and reached a reasonable high level of skill. To be a good starcraft player, you need to be skilled in three broad areas

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- Good mechanics and multitasking

This is your ability to have your units do what you want. You want unit X to go to place Y, you are quickly able to give that command, without taking up much of your attention. You're also able to simultaneously build units, advance your build at home, harass your opponent, reposition units, look at the minimap, and micromanage where necessary. Top players can have more than 5 actions per second average.

- Good micromanagement and tactical skill

For example, your ability to spread your units to take less damage from area of effect spells, focus fire on the most important enemy targets to get them down faster, your ability to position your units for flanking, to keep a scouting unit alive while being chased, etc. Maximizing the effectiveness of individual units.

- Good macromanagement and strategical skill

Your ability to advance your build at home correctly (what most effectively counters the opponent), to spend all your resources and not have it stack up in the bank, to choose the correct timings for expanding across the map or amassing an army, and to anticipate your army composition for what your opponent will do.

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If you expect to be playing a game of chess, you'll be far behind even in the first few minutes. Your opponent's scouting unit micromanages and interrupts your build without your being able to kill even the scouting unit, and while your concentration is on the harassing unit, your opponent, who can multitask, executes his build perfectly.

Without a base level of competence mechanically (which in starcraft is about 2 effective actions per second) you cannot even compete strategically.

All three of these areas impress viewers which makes for a very 'spectatable' game.

Good mechanics and multitasking are evident when, after you've watched a battle, you can see how many more units the top player has been able to produce - while he was simultaneously micromanaging his units in battle.

Micromanagement, at least in starcraft, is very fun to watch. You can see the small army outmanoeuvre the larger enemy by individual control of units - it's hard to explain why it is impressive in just words, but the joy of watching good micromanagement is a core feature of spectating starcraft games. Watch for example here, how the player's marines dodges the spines while he keeps shooting.

https://www.youtube.com/watch?v=kQtPMLOctBg

Starcraft has a lot of 'soft counters' - units that counter other units but not completely. The focus on soft counters rather than hard counters gives players a lot of strategic freedom. Even if one player's units are countered, he can micromanage them and come out ahead. Or, for example, a player can take a risky early expansion to extra resources and rely on micromanagement of his few units to stay alive.

Finally, since the maps that people play on do change, it takes a while to find the optimal builds, so you do see a lot of really innovative strategic play that people love to watch. I really cannot give any examples on this without explaining many more details about the game. I am interested to hear why you think Total Annihilation would have more sophistication.

I must admit I haven't played many other games, but I have heard people complain that either the micromanagement or the multitasking aspect are not as much on the foreground in other games, and the combination of strategy + intense multitasking + micromanagement has kept starcraft exciting for both players and viewers.