Metropolis-area dry cleaners have had a steady increase in business

Yeah, good question - note that the main fact we have that suggests that this is a good idea is about the industry/market as a whole, but not about Neuman's specifically:

Metropolis-area dry cleaners have had a steady increase in business over the past year,

So the real gap in the argument is whether Neuman's is a part of this steady increase or not (for example you could say that "sales of mobile devices has surged since 2006" but if it's mostly iPhones and Samsungs, then it doesn't mean that Nokia is doing better today than it was back then).

With (A), note that it specifically calls out that even though Neuman's market share (percentage of all the city's business) is down, its stores are always busy. This mean that there's sufficient demand for what it's doing. This is likely evidence that the plan will work (if you're maxed out on capacity today, then adding capacity tomorrow seems like a good idea), but at the very least it doesn't weaken the argument.

With (E), there's evidence that Neuman's is not part of this surge: business is booming everywhere but Neuman's is less busy than it used to be, showing that it's not a beneficiary of the surge. If it's not maxing out its current capacity, there's no reason to believe that adding more capacity - without any other changes, as the last sentence shows that it will not make - will lead to an increase in business.

So basically the difference: (A) shows that Neuman's is part of the trend or at least as busy as it can handle right now. (E) shows that it's not part of the trend, and therefore can't expect that more capacity will help it capitalize on that trend.