Probably because Tesla sells about a million cars a year, including the worlds best selling car (Model Y) since 2023. The stock consistently performs well as well, I know they outperformed estimates for last quarter. Being positioned well for autonomous driving presumably helps hold the stock up, but I don't think that's the core of the valuation, and Waymo does a fraction of what Tesla does. Waymo is impressive, but their 2025 revenue was ~350 million.