It's perhaps the single worst database in the world; with no type control, no relationship management, no data safety whatsoever to speak of (it even actively mangles your data), its interface is utter madness, and yet - it's the most used database in the world.
It's perhaps the single worst development and runtime environment in the world, obscuring code, making reasoning about code and relations between code almost impossible, using a very obscure macro language that even morphs between different computers, and yet - it's the most used development and runtime environment in the world.
It's perhaps the single worst protocol/data exchange format in the world, with dozens of intentionally obscure, undocumented versions, insane format with surprising limitation (did I mention it actively mangles your data? - it's worth repeating anyway), supremely inefficient, and yet - it's the most used protocol/data exchange format in the world.
I can't really think of anything in the computing world that has done as much damage as Excel.
What frustrates me the most about this is I've seen some insane excel wizardry from the accounting department at various jobs over the years that is effectively programming, and that if these people had put just as much effort into learning Python & using a database, they'd be better off and might actually make good developers. In my view, Excel ends up becoming sort of an artificial barrier to departments outside of IT being able to make business software.