This is the key to everything in draft position. "More important" is generally meaningless when it comes to drafting (except maybe the difference between QB and punter) - it's all about supply of people that can do the job "well enough". You have to have a starting lineup (and preferably a depth chart) made up entirely of players that can do that job well enough to win or you have a major exploitable weakness and you lose unless the opposing coach is Adam Gase.
RBs don't get drafted high not because they aren't an important position, but because there are far more people out there that can do the job well enough to win than there are spots on NFL rosters. The difference between an elite and an adequate RB is substantial, but not enough to make up for the difference between an adequate and an inadequate OT. That's why only stupid teams pick elite RBs when sure-thing (even if just adequate) OTs are on the board if both are a roster need. WRs don't have quite the glut of talent to roster position that RBs do (likely because you need more WRs on a roster), but the supply to demand ratio is still favorable enough that taking a WR when you also need an available OT is basically a giant neon sign pointing out which franchises are still run by people that could not possibly have achieved their current position on pure merit.