That’s because of 2 main factors: (1) They are almost all owned by large corporations - yes, even the “left learning ones” - and corporate ownership always imparts a right wing bias simply because the people in charge are wealthy and want to only get richer (it’s basic self-interest); and (2) Right-wingers “take the bait” faster and more widely, which translates to more views, more ad revenue, etc. (see #1).