Tesla designs chips, builds software, sells solar panels and home batteries, operates a global charging network, sells insurance, etc in addition to just manufacturing cars. It also sells and services its own cars, as opposed to the franchised dealership model under which most other OEMs operate.
Therefore to make a fair comparison you'd have to add in the rest of the global automotive supply chain, not just the OEMs. Add in the valuations of all the dealers and retailers on Earth (some of which are publicly traded), add in Nvidia and other chip makers' automotive businesses, add in the market cap of Waymo, Cruise, Zoox and all those major hardware and software players that plan to compete with Tesla's Autopilot / FSD software. Add in the market cap of all the charging networks in China. In an apples to apples comparison Tesla's market cap would be less than one third of the global market.