I did work on making a database myself, and I must say that querying 100TB fast, let alone storing 100TB of data, is a real problem. Some companies (very few) don't have much choice but to use a DB that works on 100TB. If you do have small data, then you have a lot of options. But if your data is large, then you have very few options. So it is correct to be competing on how fast a DB can query 100TB of data; while at the same time being slow if you have just 10GB of data. Some databases are designed only for large data, and should not be used if your data is small.