Because you can't see an attack happening so it's too hard for most people to use their imagination constantly. Fire, water, someone punching you in the face, those are real things. Someone defeating your firewall and engineering your password to get decrypt some of that beautiful data which you should have salted but didn't cause you couldn't pick the right flavor...that's too many layers of abstraction.
I think and practice security but realistically I know I have a much bigger attack surface than I ought to because I just can't be bothered to to run around chasing after every possible vulnerability. Frankly, it's too much work.
If bad actors get access to your computer, the downside risk is potentially huge, and you might think that would incentivize people to spend more time and effort on security. But security isn't productive or consumptive, it's reactive and people don't want to be in a constant state of anxiety.
for cars people have lojack, for houses and babies they have cameras, for bikes they have locks, and for computers.... they have nothing
All the other things you mention are easy, install/purchase once and then they mostly just work* with minimal overhead. I totally agree with you about the value of something like the SOLO but that's subject to a few problems; physical connectors are different on different devices, the easier it is the use the easier others can use it or force/trick you into unlocking your stuff, and most people don't have the time or know-how to assess the open source stack and verify the truth of its security. I have been interested in encryption technology for 25 years and am moderately knowledgeable about it but when I OK the latest update to Signal or an operating system I'm basically doing so on faith.
* Cameras are in-between security tools. They can help you but also be used against you as part of an oppressive surveillance society or actually create the incentive for people to come after your data. I've had police come to my door before asking to see my camera footage to identify suspects in a crime that happened near my property. I declined but most people do whatever they're asked without thinking much about the consequences.
To improve security, don't get into an unwinnable arms race about how can design the best lock. Make better tools for system administration that quickly and intuitively represent activity patterns so that people can notice unusual modes of access. Do so without interrupting people to death - you don't judge the health of a tree by counting the leaves, and if the leaves of a tree show signs of poor health you don't catalogue and measure them unless you're a biologist.
We need much better representations of what is going on inside computers and how data is flowing. Right now if I want to know what's happening on my TCP ports I get a list of processes and ports which I need to either monitor until I get square eyes or automate triggers on. Could you imagine telling people that the first step in dealing with a pest infestation was to make a list of every lifeform in a house and then filter that for ants or mice? Ridiculous. Why aren't there graphical traffic/packet monitors that make the backend of my network stack look like a videogame that I could actually get interested in and enjoy playing? Right now for security tools 'graphical' generally means it has a GUI and maybe a bar chart or cuddly icons - if you're lucky. Real time animations of data flow don't exist outside of movies, despite the fact that almost every computer has a decent GPU and there are fantastic free and sometimes open videogame stacks available.
People will get engaged on security when they can see what's going on, and by that I mean seeing things represented in a 2d or 3d virtual environment that doesn't require deep forensic knowledge to interpret and interact with - like a videogame. You don't need to write code to pick up, enjoy, or even be great at a videogame, although it might get you interested in code or coding ability may help. And I don't mean some stupid game like picking out which tiles show vehicles in a captcha, but a responsive environment whose parameters are mapped onto system internals in a way that makes it easy to notice intrusions and disruptions without necessarily understanding them fully.