Commentary for Makkot 47:18

And he established them [the commandments] on eleven - For in the beginning, they were righteous and could accept upon themselves the yoke of the many commandments, but the later generations were not so righteous, and if she would try to keep all [of the commandments], there would be no person who could merit this, and [so] David came and established them [the commandments] etc. in order that they merit if they would fulfill these eleven commandments. And, similarly, at every hour, the subsequent (lit. lower) generations would continue to reduce them.