Typically, they require specialized database administrators whose primary job is to tune the database and keep it running.
Many businesses, even of moderate size, reach point where they will need to purchase expensive hardware (million dollar RamSans and expensive servers) to optimize the performance of their database because partitioning databases is challenging.
So the overhead of running an Oracle or Sql Server database is quite high.
There is huge room for improvement with these traditional database products. If someone made a good cloud database that supported the same feature set but with lower administration and maintenance costs then that might be a better option.