Glyphosate is not considered a selective herbicide. It’s a borderline freak of nature that some varieties of corn can tolerate it.
Roundup is a lot cheaper than Axial Extreme + MCPA or Velocity M3 or Tandem or Rexade.. and, TBH, Roundup isn't tha good at killing a lot of the weeds that those other products kill very well. It's just not as simple as you might think.