They are if the way you monitize your platform is by offering it as a managed service, as is the case with MongoDB. Company A spends 75% of it's resources developing a product and 25% on a platform, Company B spent 75% of Company A's budget just on its platform and uses A's product for free. Who will most likely have a better platform that they can offer at lower cost?

In the AWS case, Amazon already spent many multiples of MongoDB budget on their platform, so they were easily able to undercut.