Not only crypto assets but also fiat money are stolen in the online environment. Who do you blame here?
Most of the times we destroy our own security because of our own reasons. If you can't keep the keys to where you keep your assets, there is definitely a chance of theft. I would say if you have a lot of assets then definitely use a hardware wallet.
Let me say that I was so surprised when I read the OP, we are in a porous world where everyone is desperate, so anything can happen, especially if we loose guard. You can imagine those who would be careless with their seed phrase, password and even their gadgets, their coins can be stolen of course, and this will be easy for that matter.
Needless to say, online stealing and hacking are also possible, and guess what, most of them would disappear into thin air and they will never be found. You can see that it is in two categories now, one is self carelessness, while the other is a heist. The second can happen to anyone no matter how smart you are, we should just pray that we are not a victim of such. And these days when we have the service of mixers and tumblers at our disposal, to change the assets to what you can't even imagine can be so easy, which also aids fraudulent acts on the internet.