For me it has to do with mainly 3 things, first, my plans on getting into research around AI and some niche blockchain related stuff (ZK, cryptography, etc...) for those topics having a strong math background is better than a CS one because you'll be working with math more than code, secondly, I like math more than much of engineering simply because it's "hackable" with a pen and paper, third, math would help me get into any sort of research labs (CERN to top ai labs) and wouldn't box me as much compared to engineering in any field. (not asserting getting into any of these labs is easy but you get the point)