I don't want to be held accountable to all of my previous ideas. I want each conversation to start fresh with the context that I provide. If I am exploring some library in one language stack and then I later want to look into something completely different, I don't want the conversation polluted by what it thinks I want based on the previous discussion.
I suppose for those who use it as a companion the memory is a core element. But when used as a tool it gives a significantly worse experience IME.
‡ I'd tried logging in recently and immediately it started nagging me to upgrade. Went back to using without an account and bizarrely the situation is far better.