The mistake that you make is assuming Amazon is a "low margin retail business" like how Tesla just "sells cars". The valuation is based on the belief that companies like Amazon will continue to expand based on more foundational and fundamental principles. Amazon's thing is becoming the platform and de facto distributor of everything. Keep in mind, Bezos started Amazon by selling books online. Look at where it is now, and think about it what might be in ten years.

I make no judgement either way, but there are legitimate and sound reasons for why these valuations can be justified. Try to think bigger.