I come from a background in Hybris commerce which uses Solr Search. If I am not wrong, then if the data is static, Solr works better and if the data is dynamic Elastic Search works better.
Now I mostly work with Manufacturing clients (not Retail) where pricing does not change often and stock is obtained from the ERP by making a call every time. Essentially the Product related information does not change often. In such a case, trying to understand why Magento decided to go with Elastic Search? Is the reason non technical - like Solr being Community driven and ElasticSearch being Elastic driven?
Everything has its pros and cons. I'd love to hear an official answer to this question just out of curiosity, but it'll probably never come. That's my guess, anyway.