Well one is because the person who owns twitter also owns a superior product to their own offering (GM) but this seems like the last roll of the dice for 'advertisers', if Elon does what he said he wanted to do and make twitter less reliant on advertising, they'll begrudgingly come back as they are losing eyeballs for their products.

What will be key though is not just the firing or the subscription services but if Elon can bring some quality content creators on board as that's what gets you the views, it's why Mixer failed so hard.