What's the point of SQL joins if you have OLAP?

I want to understand the purpose of using SQL joins from a business analysis perspective.

Let's say I want to analyze customer data. Why would I want to pull data from multiple tables using join statements if I can use a cube or tabular model, which seem omnipresent, even excel has this functionality. I can use point and click adhoc, slicers and other filtering and aggregation which if I understand correctly are a lot faster and if I want to do a very complex analys, I can write MDX queries or cubeformulas, in the excel example.

What can SQL joins can help me with?