The problems you present seem easily managed with an option to sign up while limiting certain use cases to those using the service anonymously.
I like a limited local first design, and a “demo login” with a simulated fully featured account that I feel allow a person to make the decision to share a piece of their identity with our product without any stress or coercion.
I tried to acknowledge that they may think the sign up is necessary for them, and that is a completely acceptable decision to make. I was just pointing out that it carries the risk of turning away weirdos like me.
If I was to build something in the LLM space I would likely try to glean some answers to these questions by cold emailing the phind team to ask them what considerations went into their decision to provide their tool in the way they do.
Chiefly, a desire for privacy and anonymity. A signup will identify my interactions with an endpoint dedicated to me circumventing other privacy and anonymity measures I take such as fingerprint resisting and use of VMs and VPNs.
Also, sharing my email puts me at risk of having my email forwarded against my will or without my consent, as well as potentially clogging my inbox with endless "promotional updates".
Finally, I am unable to make an informed decision whether the risks of sharing my email with this company is worth the utility of the tool it provides until after I try it.
I think a fair response to your question is a question of its own: What do they want with my email?