During the past decade, the labor market in France has not been operat

Hey!

The present perfect tense gets used for an action (or effect) that starts in the past but continues to the present. So while it will still seem to cover a specific time period, the idea is that the time period hasn't yet necessarily come to an end. I know from your second question that this is something you're aware of, so really I think the thing to take away from this is the fact that during the past ______ is the sort of time marker that often requires present perfect (especially because of the word past--you'll often see the phrase over the past _____ paired with present perfect as well).

This leads to the second question: can you use since? Not exactly, but sort of. You can't say since the past decade, because unlike during and over, since doesn't pair as well with the word past. It could have said Starting a decade ago, but if you were to use since it would probably have to go something like Since 2011 or Since <some action in the past. Basically, since is idiomatically different from over or during, but it of course does still call for the present perfect much of the time it shows up.