It's not about downvotes or popularity.
Story, Art & Sound, and Player Behavior are easy for them to comment on. They can give rather definitive answers since the story is written down somewhere, the art and sound people mostly fix visual/audio bugs or giving us update on their ongoing animation/sound projects, and Player Behavior is usually already decided.
Commenting on balance is tricky. There's a lot of deliberation, internal testing, and different directions they are taking things. If they say something now and change it later, people are going to cling to it. A great example is the internal Zoe changes they were testing. They were toying around with no trap effect on her E and a LeBlanc-esque retool of her R, but they ultimately scrapped it. The potential changes were leaked early, but people asked about them for weeks. They don't want to seem like liars and they don't want to get us excited for changes that don't actually happen. If it's solid enough to actually talk about, odds are that it's already polished and on its way to the PBE. This is what the Quick Gameplay Thoughts threads are for.
It's also preseason. They just made a bunch of big changes to the very nature of the game, and they always try to be careful with the things they aren't specifically changing with the preseason to see how things settle. Big changes to everything besides the preseason stuff are on the backburner until they get more data from the new patch.
Sure, they could say very general things like "X champion is on our radar" or "We have nothing planned for Y champion", but that is ultimately not satisfying and would likely be covered in the next Quick Gameplay Thoughts anyway.
