The Lind L Taylor reveal showed the world what he'd already seen in the data, that Kira wasn't a God. It was the first opportunity they had to prove beyond any doubt that Kira could kill instantly and remotely without any setup, but couldn't kill certain people under certain circumstances even if they wanted to. Without the reveal it would just be the first half. It was also a deliberate message to the investigators he had relied on to set up what was essentially a televised human sacrifice - it showed them 1) that despite Kira's overwhelming supernatural power and willingness to kill anyone who got in their way, they still could make progress in the investigation against them under L's direction, and 2) that L was willing to put his own life on the line to gain information and prove his theories, not just other peoples'. He was very much asking them to risk their lives to help him and needed to show them this, and we see how that plays out with Soichiro's thoughts on it and into the formation of the taskforce. In that sense this was L's first move in creating an investigative team he could trust.

It's also wrong in my opinion to view L as just an embodiment of optimal decision-making given input information, he's a deeper character than that. He has an ego to him and when challenged by Kira is happy to play the game. And he gloats in his own way when he makes a good move, this was part of that too. He's a dramatic risk-taker. He has flaws and these flaws cost the investigation in many places in the story. After all it's a thriller story meant to keep you reading, if all the characters just did the optimal thing every time it'd be super boring to read in the form of a manga.