It always seems weird to me. I barely know you- why would I be excited? Ask me at the end of the onsite after I've talked to a number of people across a variety of roles, seen your office, heard about the work, explored the culture, etc etc.
During the initial screen, I really only know about your business, which is not the biggest factor for me.
If you were a top-tier developer, there was a >0% chance that you would be super excited about the product because you realized the pain point that it would solve for you if you were building a real-time product at another company. And that excitement or lack thereof was a useful litmus test for Firebase specifically.
I agree that "excited about our company" is not something you get up front if you are interviewing at a company that is building an on-demand AI marketplace for ML-optimized scooter rental office spaces.
For such a small team, and an early-stage company, I believe it's critical to hire people who are absolutely excited about the mission. They're not simply looking for "an employee," but a partner who believes in what they're doing, coupled with having the ability to help them do it.
I wonder if "excitedness about the company early in the interview process" is in any way indicative of on the job performance later on.
It does seem odd. Unless I'm begging for a job, you should be telling me why I'd want to work there.