Frankly, yesterday's announcement made me seriously consider whether I wanted to apply for a job working at AWS, since I expect they have many positions where you're spending most of the time working on open source code like Elasticsearch.
The argument you're making is equivalent to the old argument against open-source software itself: if companies can't make money by selling proprietary software, who's going to want to be a software developer? Sure, it's great that some bored Finnish guy wrote an OS that's competitive with Solaris, but if he drives Sun out of business what's the guarantee anyone else will want to work on his OS? Don't we need proprietary software companies to ensure that quality software gets developed?