I think the biggest issue here is what we determine as “Success”. If by success we mean climbing the ladder to eventually becoming a high-ranking official in a company versus landing a good paying job and being able to convince management to create a new project to develop a new product or service you thought of. The skill sets, both technical and interpersonal, required for the two options presented do not necessarily overlap.

while you may land a job with interpersonal skills, if you lack the technical skills to do the job, your act will be exposed, and you may be sacked depending on the position.
To address the initial question, you chose BME to learn the technical skills of an engineer. You may choose a minor or major in communications that is intended on nurturing interpersonal and communication skills.

Also note that interpersonal skills and the ability to effectively communicate technical information ARE not the same, according to MTD a management training organization.

Also, interpersonal skills are learned more through experience as opposed to through a systematic mechanism described in a book. In that sense, it makes teaching it difficult. Taking on a job that requires interpersonal skills like a sales attendant may improve your interpersonal skill but that does not necessarily tie back to your ability to effectively communicate.
The degree is not a waste, but you are getting what you signed up for. If you learned mainly interpersonal skills in your four years, then you wouldn’t know how to do what you are supposed to do.