Just a guess, but maybe it's because electric hand planers are already capable of hogging off a lot of material fairly swiftly, allied with the fact that you'd really want a swappable cylinder to avoid all the setting up malarkey every time you changed modes.
They rip like hell though, because the blades are dead square. I'd think a slightly curved blade would fit the existing block and not be so prone to ripping - the speed at which they remove material maybe it wouldn't need to be so pronounced as a scrub blade on a handplane?
Power planers aren't the best for large flat surfaces, they're designed predominantly for planing anything narrower than the planer itself. On a large surface they gouge material out and they generally make a large mess of the work even if all you're wanting to do is scrub material off as fast as you can. Lou's video shows you how to make a power planer far more accurate and better suited for the task of scrubbing by a few little alterations such as grinding the corners of the knives, which makes a massive difference.
You know... it never ocurred to me that a power planer might need tuning, despite having fettled my er.....17 (??) handplanes. I've not touched mine for years now and didn't like it then either, but I do have some boards covered in old tar and allsorts, so maybe I'll unearth it, tune it a bit and grind off the edges of the blades.