Such "infra projects" are like, much like, the Desertech scam, a project to deliver p.v. from north-Africa to Europe able just to detour significant amount of public funds to a small set of private players. This one is just a bit smaller but essentially copy the same plot.
Other large infra projects, nearly 99% of all large ones, results in public money black holes for very limited results. At a smaller and more technical size we have had a period where anything must be big, after we learn that many small things are better than few big ones, that's happen for ship (with the sole exception of tourism), planes (777/A380 fiasco), giant road infra and so on. No conspiracy, at least if your vocabulary do not classify "economy" as "conspiracy" and rationality as plot.
Did you remember why we have switched from mainframes to cluster?
No, this is not 'normal prudence', it is completely off-the-wall conspiracy stuff. If you think this is normal then that is really problematic.
What you call conspiracy is normally named classic strategy by all who study and use it. So any normally prudent State do it's best to avoid creating potential threats potentially used against itself. Some do not just because those threats are corruption-fueled economy. And again we see countless examples in just the very recent history.
The cases you list are the exceptions, not the rule. Fact: undersea optical cables would be trivial to destroy. But as a rule they work well. Fact: water infrastructure, gas infrastructure and power infrastructure is vulnerable. But it actually works quite well. Fact: logistics infrastructure is fragile, as are most buildings. And yet, most of it seems to hold up quite well. Ok we get the occasional crazy person but that doesn't mean society grinds to a halt or that we are going to re-do all of our bridges, crossings and foundations.
