If you're a startup and use AWS, and face a competitor that isn't, chance is you're going to be blowing money on infrastructure 2-3 times faster than your competitor. For some companies that won't matter - if e.g. your hosting cost is dwarfed by your development cost - and then it may be worthwhile to pick them.

For others, e.g. if bandwidth is a large part of your cost, picking them will mean your competitors who go with other providers will be able to sell well below your cost and still have a healthy margin.

Avoiding them (and Google Cloud and Azure) is often essential if you want to survive.