I asked a similar question almost a year ago, Why would someone own a 3d printer?.
Is the answer different? In my limited experience, yes. You can make a lot of useful things with a laser cutter, but it’s not as trivial to own as a 3d printer. To begin with, the laser cutter is far more dangerous to operate than a 3D printer. Most of us think of cheap red laser pointers when we think “laser”, but those a far cry from a Class IV “cutting” laser that can sever a finger or permanently blind you.
Oh, and it’s invisible. An invisible laser that can permanently maim or kill you. Thus the various safety interlocks that prevent the machine from operating when the door is open, just like a microwave oven.
That being said, I think laser cutters are in the same class as “professional” 3d printers used in manufacturing. It’s probably not something you would own as much as something the local co-op or library or commercial printing shop would own, maintain, and use for you. When you need a stack of flyers printed and go to the local print shop, they run the machine for you, it’s not going to be much different than that.
The other issue is finding a place to use it safely. Laser cutters are safe to operate in self-test/alignment mode, but as soon as you start cutting and etching you run into the problem of toxic fumes.
Most of the media I’ve seen go through a laser cutter has been acrylic, polycarb, and other plastics — all of which generate some seriously nasty fumes when they are etched or cut. My experience is that the warnings in the Plexiglass(r) MSDS are %100 correct. Not only do you need space for a laser cutter, you need an exhaust fan that can move a lot of air outside very quickly. (The commercial Epilogs I’ve used had fans that were loud enough to drown out normal conversation, I don’t know who specified them so they might have been overkill.) Cutting / etching wood has similar problems — lots of smoke from the wood and whatever byproducts come from burning the glue if you’re cutting plywood. Paper’s not really a problem, and cutting PVC and some other materials will actually destroy the lens so those aren’t cut in the first place. [Edit: When laser cut, PVC releases free chlorine gas which combines with atmospheric oxygen to form hydrochloric acid which is bad for the mechanicals. I suppose If you had a laser cutter filled with an inert gas it only be a matter of safely disposing of the exhaust gases.]
So going back to the original question, I think the answer for now is “because they can”. If you have the space (a big garage or a studio/hackerspace) and time (I’ve got 50+ hours into my lasersaur build) it’s certainly an experiment worth trying.