Threads only shows users who have signed in to Threads. If you mention an Instagram user in a Threads post that has not signed in to Threads prior, the mention is removed because it’s not a valid handle.
I urge you to read through the link in the original post to the Mastodon user who originally made this claim, where you’ll find plenty of people more eloquent than me explaining why this is inaccurate.
If it’s so obvious why can’t you state it clearly?
It seems like the insinuation is that Threads is artificially inflating user counts with “shadow accounts” that aren’t real - however it’s been clearly determined that they aren’t.
So, if it’s not that, then, again… what’s the “so obvious” point I’m missing?