Just like how social media companies suddenly grow a spine and do something about bots and troll behavior only after they become large and successful.
You can't get people to join if there isn't a lot of people, and there isn't a lot of people because nobody joins.
Faking the participants 'till you make it is cheating, compared to an organic growth that rarely happens at the inception of a new platform.
The amount they are doing about bots, trolls, and outright state-funded dezinformatsiya and active measures warfare being waged on their platforms is only the absolute minimum so that they can claim to be "doing something", and not appear to be fully and actively allied with the assaults on democracy.