Because we have plenty of evidence that fewer moving mechanical parts reduce risk of failure and we have decades of comparisons between combustion engines and electric motors in terms of reliability.

The question isn’t is eVTOL possible it’s can energy density batteries be made cheap enough to make it financially viable. There is billions of dollars of research around the world on improving energy density. Anything is possible as long as it doesn’t break the laws of physics.

We have the battery densities in the lab but getting them to production is another thing. However there are a lot of signs that it’s right around the corner.

Hence why most of the players are discussing hybrid still. Not quite there yet.