Everyone can name a stretch of highway they've seen treated this way, and this explanation just doesn't cover it.
You don't know just from driving by whether 99.9% of projects are quick and efficient.
I think there's an inherent bias here. Each individual is not seeing that section of road 24/7. At most they see it for a few minutes (or perhaps a little longer, if traffic slows enough), maybe once or at most a few times per day. That's a very small fraction of the day, and work could be occurring during other parts of the day, possibly even at night. Safety might require that they do the work when there are few cars driving by, but the nature of the work might be such that they can't unblock the lanes during the day.
I get that this isn't satisfying, but often reality isn't. And I have no doubt that there are plenty of mismanaged projects around the world where there are lots of delays, and long stretches of time when nothing is getting done. But I think it's incorrect to believe that nothing is getting done just because a few people you know drive by the area a few times a day and don't see anyone working.
It also tends to be the case that price is reduced by scheduling work across multiple contractors with independent scheduling... so the cost savings come at the expense of idle periods while waiting for the next contractor to be available. Not a totally unaddressable problem but ultimately fast and cheap are, as usual, opposing requirements. Funding politics can also play a role here, very common that larger projects don't have all of their funding available at once, so they may sit idle while waiting for the next set of funds.
Practical Engineering videos on road construction and public works https://www.youtube.com/watch?v=PIK6I6Q58Ec https://www.youtube.com/watch?v=22W5tRWbUVI
The problem is that both the workers and the equipment are short in supply.
The cause of that is the lack of continuity in politics. Construction machines and staff training can easily reach dozens of millions of euros in cost - particularly when it's rail related. It would be financial suicide for any company outside of extremely large conglomerates to take on that risk without politics providing the guarantee of at least 20 years worth of projects to recoup that investment. Instead, the US is down to "we can barely plan for the next fiscal year" timeframe, and Europe to "we can barely plan 5 years until the next EU fiscal cycle, add national election cycles and you're down to 1-2 years as well". On top of that come government accounting clusterfucks - basically, the norm is that it is very difficult to transfer budgets from one year to the next, and when you don't use all your budget for whatever reason, next year's budget will be cut back.
For any one stretch of road what percentage of the time is it closed in this way? Or in other words, what is the SLA of the road?