Hell, the stock market goes offline every night.
Those last % of uptime are very, very expensive at every level (money, people, logistic...). They better be worth it.
HA is not just about getting that sixth 9, it's also about the peace of mind that you are insulated from a range of problems. Not only would I not worry about our SQL service going down, I also don't have to worry about what I have to do when a node goes down, because that's automated.
But the cost of a 500 is always to be balanced with the cost of going full throttle with micro services.
As perfectionists, it's easy to fall into the trap of choosing the later by default.