You don't understand at all. Elastic starting monetizing it, not Amazon. They raised over $100M in venture capital. [1] They had a $2.5B valuation IPO. They made many features available through subscription only for over 5 years. [2] This is in contrast to the Apache Solr project, where the updates to the engine are made to the open source project and it is released in concert with Lucene.

[1] https://techcrunch.com/2014/06/05/elasticsearch-scores-70m-i...

[2] https://www.elastic.co/blog/shield-know-security-coming-soon