Because it's extremely easy to damage other people with lasers. Stray reflections can easily blind. It's one thing if you're in an enclosed space only able to hurt yourself, but most of the real world is not like that.
Agreed, and that's to say nothing of the speed at which blindness can occur. Then there's those pesky IR lasers which at the right class level can blind you in wavelengths you cannot see[0].
[0] Which to me has always been one of those "hard to believe things" and, indeed, I've never worked with an IR laser or tested this (nor would I be interested in doing so) but I can't think of something more terrifying (related to blindness, anyway) than walking into a room, looking at something, seeing nothing particularly interesting and then ... seeing nothing at all ever again.
To emphasize this point, since we're talking about a 450nm laser at either 500mW (maybe just barely low enough to hypothetically qualify as Class 3B?) or 800mW (probably Class 4?), any stray reflections could easily cause blindness before the eye can respond by blinking.
Any laser powerful enough to burn or cut is a "why did my eye make a popping sound"[1], risk, not the "blink oww! that's bright!" that we are familiar with.
[1] the sound is a spot on the retina explosive boiling after the laser heated it extremely rapidly past 100C
People endanger the public at large all the time, knowingly or unknowingly. There is no decent world in which acts which merely pose a danger to the public are illegal before they cause that danger.
People instinctively understand the risks of throwing things, even sharp and heavy things. People do not have an instinctive understanding of the risks of lasers. They may both be dangerous, but that does not mean the two levels of danger are the same.
[0] Which to me has always been one of those "hard to believe things" and, indeed, I've never worked with an IR laser or tested this (nor would I be interested in doing so) but I can't think of something more terrifying (related to blindness, anyway) than walking into a room, looking at something, seeing nothing particularly interesting and then ... seeing nothing at all ever again.