1. The scope of the change. My understanding is that Elasticsearch may use Lucene under the hood, but extends it in ways and for use cases that Lucene was not designed for. The same can not be said about AWS taking Elasticsearch and running it as a drop-in replacement.
2. Perhaps most importantly, Elasticsearch didn't build on top of Lucene, and then decide to call itself Lucene. If you think there is so little differentiation between the product you built and the product you built off of, that you are better off highjacking the name, then I question if you made any meaningful differences.
3rd BONUS difference: It is my understanding that a large part of the core Lucene team works at (or at one point worked at) Elastic[0].
1. No one says you need to modify/extend something in order to sell a service around it. That's why we have licenses that list exactly what you can do and cannot do with the software.
2. Amazon adds value here by providing hosting solutions for companies using the elastic search software. So it makes sense to call it "Amazon Elasticsearch Service" since that's what it is. I think interpreting this as Amazon built a new competing product but calling it the same name is not the right interpertation. If that's confusing then maybe modifying it to "amazon elasticsearch hosting service" would be the OK thing to do. Not sure if that would make Elastic happy.
3. That's nice of them (really!). Sounds like win-win. But again, it doesn't make anything they do more justifiable.
There are two main differences here.
1. The scope of the change. My understanding is that Elasticsearch may use Lucene under the hood, but extends it in ways and for use cases that Lucene was not designed for. The same can not be said about AWS taking Elasticsearch and running it as a drop-in replacement.
2. Perhaps most importantly, Elasticsearch didn't build on top of Lucene, and then decide to call itself Lucene. If you think there is so little differentiation between the product you built and the product you built off of, that you are better off highjacking the name, then I question if you made any meaningful differences.
3rd BONUS difference: It is my understanding that a large part of the core Lucene team works at (or at one point worked at) Elastic[0].
[0] https://www.elastic.co/blog/investing-apache-lucene