I actually think one thing creating the big drama with this is: Aiyuk actually wants to stay in SF. He just wants more money, because of the WR market, than SF is going to pay with the upcoming cap ramifications. If he didn't want to be in SF, he'd already be in NE or CLE. Yes, he's hoping maybe he can thread a needle to Pitt and maybe that will make everything ok, but what he really wants is for the Niners to pay him 30M. He loves Shanahan. He loves Purdy. Seriously, he strongly defends Purdy constantly to everyone, even at times when he didn't need to. He likes the organization and he's even ok with his role. But, he wants the WR market money.
So, I think he's still having a crisis personally of what to do. You saw it with his reaction in that "they don't want me" video from earlier this summer. I bet he doesn't even really want to go to Pittsburgh, he wants the Niners to blink. And there's precedent. They definitely blinked with Bosa, and paid him everything he wanted.
But, edge rusher might be the second most important position in the NFL these days and WR isn't, and it's really not in Shanahan's system. So, he's stuck not knowing what to do. Otherwise, we'd have resolution already.