You haven't answered anything interesting. Any software system that anyone cares about operates on state - user documents, a database, other bespoke systems etc

You haven't answered anything interesting. Any software system that anyone cares about operates on state - user documents, a database, other bespoke systems etc. If the operator of that system accidentally deploys malware to it, how to you ensure that this malware doesn't destroy, replace, or exfiltrate this state the the system normally operates on? Malicious code doesn't need to run as root in order to completely destroy a business. Not to mention, all of the things you describe are very nice if the kernel is perfectly secure. But it's not, so it's always possible and even likely that compromising any user on the system is equivalent to compromising root. And if you compromise one system, you can then exploit bugs in other systems' kernels that might allow RCE through well-crafted packets or other exploits that gain access without running through any user-space code that might validate those attestations. And finally, when a vulnerability is found allowing such exploits, you now need to update all of these readonly systems - and this happens at least once a month. Do you go with a USB stick to each of 10k systems on five continents to update them? This kind of smug "I know better than the rest of the industry, security is easy if you do things my way" is rarely productive or applicable.