When citing Sturridge's transfer history, I think we need to consider the situation at City at the time he left.
When his contract expired at City in 2009, he was just 20, and at a time when money was just pouring into the club, with expectations of greatness and quick returns. The manager at that time was Mark Hughes (of "I'll spend a lot getting shit results" fame at QPR). In the 2008/2009 transfer window, Hughes' attacking purchases included Robinho, more experienced players like Bellamy (whom he'd worked with) and SWP, and of course, the superstar that's Jo (hahaha). The following season (2009/2010, the summer that Sturridge left), Hughes further loaded his team with the likes of Adebayor, Roque Santa Cruz (again, another familiar face for him) and Carlos Tevez.
Unless Sturridge was identified as potentially a better player than the likes of Adebayor, Tevez, Robinho, Bellamy (familiarity with Hughes) and Santa Cruz (familiarity with Hughes + one great season at Blackburn), etc., I don't think City were going to be too fussed about losing him at that time. Doesn't mean he's not a good player; they just couldn't give him the time/space to develop. Unless he was superstar potential (which we know he isn't), it just wasn't going to happen.