Because Amazon has 1.2 million employees, $386.1 billion yearly revenue, and $20 billion yearly net income. Tesla has yearly revenue of $31.5 billion and net income of $721 million. Presumably people think that Tesla is priced for explosive growth, but Amazon has also been on a growth tear that shows no sign of stopping, so the basic premise that Tesla at less than 1/10th the revenue and 1/20th the net income is worth half as much as Amazon seems fishy.