"If the answer is yes, then why?"
I know this won't be a popular answer, but their core RDBMS is the best in the business for high end relational applications. There's a reason Sybase, Infomix and DB2 all fell by the wayside with only SQL Server trying to keep up.
And no, NoSQL DBs are NOT a suitable replacement in most circumstances where data relationships matter and can be of N degree complexity. Trying to do even moderately complex data queries on Mongo is like pulling teeth from an angry lion.