No reason, except for the expense and time spent getting it dialed in. I'm condensing your own words in your post, but you are mentioning those things yourself.
Fair enough, especially as to cost. Time and tuning are part of the hobby for me. That's why I went with the Microsquirt as opposed to a more self tuning option.
PS my garage (and I) never smelled like gasoline in any carb'd car I've owned, including the one in my sig pic. If a gassy smell is coming from a car, blame the person in charge of tuning it, not the technology, or lack of it.
No doubt. I will gladly admit that I suck at tuning carbs. :-)