Yes, the game is called Seaman. Yes, you do use the microphone attachment to talk to the sea man. Yes, the narrator is Leonard Nimoy. I don't make the rules, but I would like an explanation.
On the fucking Dreamcast, no less. This game existed in 1999 and was more interactive than half of the bullshit LLM AI chatbots currently on the market.
The explanation is that in the 90s things like Call of Duty franchising or WoW addictiveness feedback loops or being nickeled and dimed by excessive micro transactions didn't really exist yet, so publishers had to take risks on weird and innovative stuff, especially on disc based systems because printing discs is dirt cheap compared to cartridge manufacturing.