Just because you can, doesn't mean everyone will rush to do it. This is a self-service platform. Putting the data in the hands of decision makers. There is hierarchy in how people use such software:

The user: He uses only the apparent features in the GUI. Like the grid and aggregation formulas in Excel. He learns how to use the software from other people showing him how to do stuff.

The Power User: He has deeper needs, but can only be bothered to use features 1 or 2 levels deep in the GUI. Like pivot tables, vlookups and index/match, logical operator formulas in Excel. He learns how to use the software from tutorials.

The Advanced User: He has a task and does not mind getting his hands dirty in order to fix it. Uses DAX and Cube formulas. Perhaps even Macros. He learns by googling his problem and reading documentation.

The Developer: Solves the problems at the programmatic level.

Tableau occupies a very specific spot. It is brilliant for the User who only consumes dashboards via clicking on them. No explanation needed and it is super polished. It is also powerful enough for the Advanced User who can perform relatively sophisticated analyses from the interface. Generally speaking, it is not a good fit for the Power User who doesn't have the need to justify using it. It is also not a terribly good choice for the developer because it is too restrictive and the programmatic features are not well thought out.