Building them like that any more wouldn’t enhance shareholder value.
This s a big problem for many organisations. 99% of the time it's not cost effective to spend money on making it that little bit extra resilient. The remaining 1% gets expensive, fast. It's a gamble, and most in the C suite take the gamble that it'll happen when the next person has taken over...
I've trained in emergency response when I lived in the UK, and I've been working on high availability systems design since the last millennium. I frequently get told I'm paranoid. I sometimes get to say I told you so.
I've seen a lot of companies doing disaster recovery exercises, and they are almost always a disaster. COVID has made clear that a lot of organisations have a very poor bus factor (number of staff you can hit with a bus before you can no longer operate). I know that in the safe at work there is an envelope marked "only to be opened in the event of Julia's Death". Because someone has to be able to pick up my tasks.
We've seen what happens when Facebook break their network and discovered that everything was dependent on it. Partly cos "eat your own dog food" and partly cos "it should never fail". I spend far too much of my working life asking what if, and what do we do to minimise the impact.
The phone network is a critical safety system, and maintaining that level of service really should not be at the whim of share holders value.
J