Sterak's provides the buyer with unique interactions is the big thing here.
A) It provides squishies an anti-assassin safety net
B) It provides bruisers and tanks an incentive to taking damage in order to maximize their own damage output.
Also who says you can't get Titanic AND Sterak's? I usually do with Poppy. Frozen Mallet is still pretty situational though. The slow is typically only useful on heavy AA'ers and is outclassed by
for almost anybody else, while only being truly useful when you need to slow somebody without dashes and isn't immune to slows (... Not a lot of champions)
We can't just look at Gold Efficiency when you're looking for what counters what. If Zhonya's ONLY had the active and no stats on it, people would still buy it to counter
. It just so happens Sterak's is providing that same niche for AD champions.