In spite of drivers being non AGPL, companies with 'absolutely no AGPL' policy cannot try the open source version of these DBs which puts these products behind others. I don't think AGPL provides any real benefit for the vendor. Most small organizations will want their patches (if any) to be upstreamed so they don't have the maintenance burden. Most big organizations will want commercial support anyway. All AGPL does is discourage adoption.

There are plenty of non-AGPL DBs out there doing pretty well. Here are some examples of GPL/MIT/BSD style licensed DBs: Riak, Cassandra, Redis, MySQL, PostgreSQL, ArangoDB, CouchDB.