Many years of head-start in terms of experience/designs/scale-up etc with EVs, brand recognition, and in the US a charging station network.
Also, they're fully committed to EVs whereas most of the legacy manufacturers seem to be completely stuck at half-assing the transition at best. It feels like (with the exception of Volkswagen Group - includes Audi and Porsche) a few of the legacy competitors are starting now and many are not even seriously trying yet. The other competitors are newly founded companies. Everyone is playing catch-up while Tesla has delivered millions of EVs.
Tesla has also bet on massive scale from the beginning (i.e. high up front costs for lower costs per unit later) whereas other companies seem much more cautious. They are also not burdened with decades of organizational cruft and ICE-focused structures that have built up in the traditional companies.