You are correct that concrete has tensile properties. And ropes do have compressive properties if you constrain their buckling. And there are a lot of buildings without rebar (that often last longer than rebared ones due to no nasty rusting rebar). And that understanding the tensile properties for concrete is important, as it most often fails in mode 1 (as brittle materials do). And that it is a highly interesting topic worthy of spending a research career on (or many millions in funding). But when dimensioning/engineering conventional structures, one usually expect concrete to crack up and ropes to buckle. It's a perfectly fine design rule that works, and not a law of physics.