Because of a shortage of expertise, many organizations opt to invoke databases as a service in the cloud. Source
Relational databases tend not to scale very well, either inside or outside the cloud. Developers can’t be sure how big those applications will grow, or how many people will end up accessing them.
Many a cloud-application developer will end up performing an unnatural act known as “sharding” to either get the database to scale or deploy more databases. In either case, the cost of managing the overall environment increases in direct proportion to the complexity of the environment.
To get around this issue, cloud developers have increasingly turned to databases not based on relational architectures. Some of those database architectures support SQL, but just as many promote a NoSQL agenda using platforms such as Hadoop, CouchDB, MongoDB or proprietary object-oriented databases. Because of a shortage of expertise with these platforms, many organizations opt to invoke these databases as a service in the cloud, rather than deploying and managing the databases on their own. For more details visit here