Try and make your sentences short and to the point. Take one of the paragraphs you spoke, then repeat it over and over and over again until you're at the point and avoided the tangents. I'm no expert but I think that's also why your colleagues stop listening, because you don't get to the point. Avoid fillers too - uhs and ums, stuttering, stop-words, etc - and try to focus on bringing your point across in a single, firmly worded sentence.

So taking your one sentence:

> I have found that when I speak, I rarely command attention and captivate as some others do. Probably something in my speech patterns. Perhaps they are slightly more apologetic / geeky / nice than others. People may interrupt me or turn away, even people who respect me.

You could rephrase (and speak) this as:

> When I speak, I rarely command attention and captivate as some others do. People interrupt me or turn away, even people who respect me.

People have a short attention span. I myself tend to mostly ignore this one colleague I have because pretty much half of what he says is filler, like, a ramp-up to his point ("so uhh, basically, like"), his main point (stuttering and lots of uhs), and end-filler ("you know?"). Mind you that he's not a stutterer as such, he just needs to make noises while he's trying to think of what to say next (like uhs). Not speaking in his native language is also a factor there.

TL;DR: Firm, short, unapologetic statements. "We should do this" instead of "Uh, guys, excuse me but, like, I think we should sorta lean towards this?"