The examples you listed makes me ask this. Imagine your parents, while raising you, given this option of having their pay reduced by 25%. How likely would the options you listed have been an "opportunity of a lifetime" to them?
I can imagine plenty of people would accept the option of taking 75% of their salary to spend all/most of their time with their young kids for a couple of years.
After tax, it might not work out to much of a difference anyway, especially after you consider the other incidental expenses relating to work (transport, attire, etc).
Of course, no agreement is going to be 100% perfect in every scenario, but this is way more even-handed than a one-way non-compete with no compensation at all.
I just had a quick look (I never had one), non-competes without compensation are illegal in France.
Another possible explanation: "I took a two-year sabbatical to work on my own projects and improve my skills".
One time I got $50k and full salary to stay on with a group that was in run down mode. I wouldn't take that option again.