"Going on an on about things" one finds interesting is not the same as marketing oneself.

I don't know if this is what you're referring to by the phrase 'going on and on' but the phrase makes me think of my coworker who talks in circles about any topic, providing many words but little info. And the circles usually incorporate personal anecdotes. He hasn't realized people tune out immediately.

OK, here's a possibly better picture from having hired many engineers over the years.

I don't care so much what you find interesting per se. I care about the intersection between what you find interesting and what my company does. I care how good you are at doing that kind of work, about your confidence that you can produce and solve problems without me needing to hold your hand all the time, and your likeability. If you can demonstrate those things better than the next guy, you'll probably get the job.

I think the interview process is tricky for people that like to dig into technical details as a lot of companies just want to hear adulation from the candidate towards the company, under the guise of excitement for the company mission. or whatever.