Bottom line when you are looking to create a corporate video, you are investing in a video that you want to work. The best location, camera work, lighting, and scripting can all be lost if an amateur is not believable or has some funny mannerisms that distract the audience from the message you are trying to convey. The audience will either be quietly chuckling to themselves or already thinking about something else causing you to lose the sales opportunity. Real people will work successfully in a video if they are company management or workers explaining their job or talking to other employees but a video to be watched by customers has the goal of effectively communicating and often real people cannot deliver. Remember, your customers are used to watching television and they will rate their video by that standard.
Using real people can be useful as background actors or as people that might only have one line to say but professionals can deliver a smooth and believable presentation. They deliver the message without "getting in the way". They work quicker, having already memorized their lines, or they use a teleprompter or ear prompter. If the scripts changes on location a professional will be able to adapt quickly. In short, the investment in actors pays high dividends in a believable video with a faster production time.