There have never been more than a couple hundred electrodes in a human brain at once. When it comes to vision, that equals a super low-res image. The Neuralink team threw out the number "one million simultaneously recorded neurons" when talking about an interface that could really change the world.

Wait but Why got weeks of meetings and details from Elon Musk and the Neurlink team.

Elon wants to get a human computer interface closer to computer to computer interface speeds.

Until the 90s, electrodes for BMIs (Brain Machine Interfaces) were all made by hand.
We began to manufacture 100-electrode multielectrode arrays using conventional semiconductor technologies. Neuralink co-founder Ben Rapoport believes that "the move from hand manufacturing to Utah Array electrodes was the first hint that BMIs were entering a realm where Moore's Law could become relevant."

If we double our total every 18 months, like we do with computer transistors, we'll get to a million in the year 2034.