Bots are parasites: they only thrive if the host population is large enough to maintain them. Once the hosts are gone, the parasites are gone too.
In other words: botters only bot a platform when they expect human beings to see and interact with the output of their bots. As such they can never become the majority: once they do, botting there becomes pointless.
That applies even to repost bots - you could have other bots upvoting the repost, but you won’t do it unless you can sell the account to an advertiser, and the advertiser will only buy it if they can “reach” an “audience” (i.e. spam humans).
Yup, I got that you don’t mean that everyone is a bot there. I just don’t think that there aren’t so many of them as you’re saying; it’s certainly not as much as half the users, or even the activity (bots tend to be more active than actual users).
They’re still wrecking damage on the place though. Eventually they’ll reach a plateau in proportion, but their numbers will go down, alongside the actual users.