Because Tesla is in major indexes like the NASDAQ composite, and S&P 500, as well as many major/popular funds/ETFs. Additionally, many funds are weighted by market cap (so more expensive companies get even more disproportionate investment). And the majority of stock investment activity happens through these investment vehicles today.
Generally, anyone who puts money into a 401k, will likely have some of it going to Tesla and disproportionately over other auto companies - simply because how funds are typically weighted.
Generally, anyone who puts money into a 401k, will likely have some of it going to Tesla and disproportionately over other auto companies - simply because how funds are typically weighted.