Meta is only pushing, not pulling. So if you’re an influential person there is less incentive to create a masto account. Threads content will appear in both places, but Mastodon content will only get exposure with mastodon’s smaller user base.
The fear is that the broader Fediverse will get hooked on a flood of Threads content. They have much more daily active users, and as we already know, large instances can easily dominate a feed. And Threads will be gigantic.

[–] Chewy7324@discuss.tchncs.de 4 points 11 months ago* (last edited 11 months ago)

To 1:

We're starting with the ability to follow threads users from activitypub clients, but we will get to the ability to follow accounts from activitypub servers on threads as well

If 2. will actually be a problem some instances will defederate, while many users will choose an instance which allows them to follow who they want. I'm all for interoperable social media/messaging, because it gives users the choice.

I'm curious when they'll add inbound federation. It could lead to massive amounts of spam, so they'll probably block instances or inbound traffic quite quickly.

Hopefully it won't end like email, where it's really difficult to start federating to the big providers (Threads). But even then, we'll still be able to choose any of the current instances and continue without them. Edit: It's not a big problem if Threads doesn't show all posts, since other instances will still show them to users who care. Compared to email where a 100% delivery rate is critical (at least for important stuff).