Social media has a very good ratio of information spreading versus effort required. It’s also why it’s a popular thing for misinformation and influence campaigns.
In contrast, if a government agency wants to make a website for this, it probably needs a proposal, budget request, approval by a commission, a bidding process, and other bureaucatic procedures put in place by politicians that wanted to lower spending.
Governments are probably a bit hesitant to go that route after a few pages like that got hacked and ended up full of Russian propaganda.