Why dark backgrounds? The short answer is because they can look awesome. Your website designer or marketer may have an idea about why they prefer certain types of backgrounds but it is rarely because they are concerned about how good you look. Fortunately, that is pretty much all I care about.
While the white background has a clean, contemporary look, darker backgrounds can look better with certain skin tones or clothes. It can make thin hair look better. I love photographing headshots with my clients wearing gray on a gray background. It looks like a headshot that would be in Vanity Fair. It looks like we knew what we were doing. It is like when an artist works with a limited color palette. It is another layer of simplification that helps the viewer focus on your expression, which is the main thing in a headshot communicating that you are confident and approachable.
I don’t think that either white or dark backgrounds are necessarily more corporate or professional than the other. They each have unique merits, and there is certainly a big aesthetic factor that reasonable people can disagree about. I am acting as a consultant for you throughout the process, so I will certainly give you my opinion.
Unless we agree to something else, I usually quickly alternate between white and grey backgrounds in the middle of a set (you may be surprised by how I do it), so we can see which we prefer.
In no event will I photograph you on one of those super conspicuously mottled backgrounds like they used on you in school. If your company insists on that, my oath to do no harm prevents me from complying.