To be honest, me. I never really liked how the Demoman could excel on both offense and defense, and his ability to lob stickies and detonate them ASAP was a large part of his offensive game. I thought it made sense to nerf that aspect in order to reign him in a bit and encourage more thoughtful sticky placement, laid in advance as traps. It also doubled by making the Demoman more vulnerable in close quarters, which makes sense given that his counter is Scout. The one part of the nerf I disagreed with was how it applied to taking out Sentries as well.
The rest of this dives into speculation with a side of ranting since I have no 6s experience, so feel free to stop reading here.
From what I understand, Demoman was limited to a single player in 6s because of a combination of high damage and simple trap creation. With 2 Demomen, a team could lock down all possible chokepoints around a given area and that's no fun for anyone. Okay, makes sense.
Now that Demoman was nerfed so that his stickies do middling damage at best in direct combat, people started acting like the sky is falling, demanding Valve roll back the change (which they did...) and some proposed a mod to do so themselves. But since the Demoman in his previous state was such a powerhouse to the point that he was explicitly limited to 1 per team, shouldn't have that been a red flag that he was perhaps too powerful? Did anyone in the comp scene suggest perhaps raising the Demoman limit to 2? (Likely not since the trap issue remains.) Or perhaps accept the idea that a 6s team wouldn't have to be Medic/Demoman/Soldierx2/Scoutx2 once one of those classes was nerfed off his pedestal? Embrace change? Explore new options? Evolve the metagame? Anything?
IDK, I'm ranting at this point, but it honestly worried me to see very little constructive feedback about the nerf. (Admittedly I don't frequent the competitive forums much so feel free to point me to reasoned arguments if they exist.) And now that it's been rolled back, I assume purely in response to the outcry, I can't help but be slightly annoyed.
Also what about Heavy's nerf? That one I can easily see room for improvement but it's been left alone.