Mongoid_fulltext: full-text n-gram search for your MongoDB models

It seems as if for every database / NoSQL solution that comes out, someone writes a full-text search provider for it; why aren't people using something full-featured and abstracted away from the data model like Lucene and not reinventing the wheel all the time?

does this scale? Just recently I was using mongoid_search and it performed very slowly on just 5000 documents, autocomplete was not usable. I switched to solr and its easily handling 100K documents as of right now. I don't know if mongo is really a good fit right now for search functionality. Id love to see benchmarks with mongoid_fulltext.