A startup, where you'd rather have your engineers working on adding features to your product instead of "managing and operating" a database? Have a lot of money to throw at this problem, being aware that you are paying for convenience? then using RDS and such would probably be a better choice.
An established company/product with a team of people working at a non-crazy pace, and catering to steady enterprise customers? Would like to build a sustainable long-time infrastructure setup that is optimised for efficiency and cost? running your own Database chosen well for your needs, backed up and tested rigorously, and managed by people who cares for the company's infrastructure would be a better idea.
It is weird when large companies with a dedicated platform team choose to run so many databases for their teams/services on a PaaS. That clearly is an optimisation opportunity.