Amazon got that reputation a decade ago when they were vigorously growing in user base and revenue. They couldn't hire fast enough if they even wanted to without wrecking the organization, so there was a ton of teams/people that felt immense pressure.

These days things have leveled out a little bit and I think of Amazon as a new IBM in the making. More corporate, more cruft, more politicking. This is especially true on the retail side, as Amazon has become so complicated and specialized that you'll have specific tech teams for handling edge cases for particular types of products. I think I recall there basically being a 'shoes' team that would implement features just for selling shoes on the site, etc.

I will say though that when I was in AWS a few years ago, that I was downright shocked at how lean some of the teams were. IIRC there were less than 100 developers that maintain all of dynamodb for instance.