It's more than that though. "Citrus" was a flavor that roasters were trying to bring out, which is fine (and interesting). However, what happened with hoppiness in IPAs happened with acidity in American espresso. As roasters' palates got accustomed to a particular roast, they needed to keep going further in that direction to create a similar flavor. Thus, escalating acidity, and the rise of the sour bombs in 2011 or so. I feel like things have tapered off a bit in the past couple years (at least on the East coast).