I would say that its because people understand how to use it.
Excel is frequently used as a database, not because it makes a good database but because people don't understand how to use Access (or any other relational database) but Excel is easy enough that they can get something usable.
That's part of it, but not all and also not the most important IMHO
Excel clones simply don't cover the breadth of functionality provided by the OG, not to mention key UX features like countless hotkeys and menu accelerators
Every Excel user understands Google Sheets. They just don't like feeling like they're strapped to a wheelchair
Often they understand Access, they just don't have it.
Office Standard and Home & Business SKUs are without it, you need Office Professional Plus. Because it costs few hundred more for just Access and Skype, most workers will get the Standard one.
You actually need to understand the basics of relational databases in order to use Access effectively (unless you are only using a single table - in which case you might as well use excel).
Many people don't need complex features of Excel, LibreOffice is pretty good. Many people have Excel and don't even get to basic functions like vlookup, nevermind anything that is actually lacking from other applications.
