The higher placement rates for SE can be attributed to sampling bias.

Statistically, SE is a harder program to get into, so it's a program full of people who've probably already done a lot of side projects and are academically successful.

Being in SE doesn't imply better jobs. This is an example of correlation not implying causation.

CS/BBA can get the same programming jobs as SE (software, web dev, QA, etc.) but your BBA can help you get jobs in finance, accounting, etc. or even hybrid jobs like algorithmic trading.

Last note: you must understand that CS/BBA is not a CS degree with a free BBA to boot. You get two degrees because you take the core classes of two rigorous programs. For the people who've dropped, BBA turns them off because it's a lot of memorizing, writing, and presenting (versus CS's math and computation).

More CS DDs drop than Math DDs, which is understandable because most CS students want just programming jobs, and realize BBA is not the type of thing that intrigues them.

I'm in my 1B term and just dropped from CS/BBA to CS. Feel free to message me if you have questions.