If a DBA works for a single organization for many years and never works outside that organization then they will only have the tools that are required by that job. So a DBA can conceivably work for 15 years and not know all the ins and outs of being a senior DBA, though they are titled a Senior DBA. If a DBA works a few years here and a few years there, acquiring the skills each unique experience affords then, as well as working with various other database professional, they learn to use a wider variety of SQL tools and master more of the techniques required to perform at a senior level.