Even if Threads is crap, it’s pretty obvious it’s gonna steal all of Twitter’s advertisers the moment they start showing ads, because the ad money generating users are moving onto Threads.
Heck, Threads doesn’t even need to show ads and the displacement of ad money away from Twitter will benefit Meta as much of that Twitter ad money will get redirected to Meta properties like FB and IG instead.
My Threads feed is full of massive brands promoting itselves already. Since you can't control the feed those are basically free ads. The only major difference will be that in the future those brands will be paying Meta for the privilege. Get the brands addicted with free engagement early on and then once they're good and hooked you start charging.
Also there's a bigger difference which is that FB/Meta ads are in an entirely different league of quality. The only ads I hear people IRL talking about actually buying and liking the products advertised to them are IG.
