Why are remote controls not used more

There are remotes for lights, ACs, DVD players, audio equipment, other things.

You can buy a remote and a few little boxes that turn AC power ON/OFF, so anything that plugs into an outlet can have it's power turned off/on via this remote.

I would not want a remote for a lawnmowers, tractors, cars, they are all too dangerous, and that is probably why you don't see them.

You can buy a robotic lawn mower (see link) for about $1200. Saw one like this in operation at Disney's Epcot back in 2000.

Remote control operation is doable especially if you DIY. Check out Make magazine which featured a how to build your own remote control lawn mower.

Engineering encompasses not only the technical aspects of a design but the economic aspects as well. I like to say "With engineering that you can design and do just about anything if you spend enough money. The question is how much do you want to spent and is it worth spending that much?"

Point is that if I spend $2000 in materials and labor to design and build a remote lawn mower what is the pay back? That two grand could be spend instead to hire a kid to mow my lawn for the next 5 years plus worth of summers just to break even on the initial expense of building such a device.

There is another saying that I use in engineering "Use the KISS method. Keep It Simple Stupid". Don't overly complicate a simple task. Consider how you would guide a lawnmower from you back porch in such a way that you don't miss any grass when mowing back and forth. It would be very difficult and would mean that you would have to spend more time mowing to ensure that you didn't miss any grass. OR spend additional money and add tele-prescence to your mower. Not only complicating the design but increasing the cost dramatically. For the money you spend to that you could get nearly a life times worth of mowing done by that neighborhood kid.