its not that jeans are indicative of religious level. obviously, mike, if someone were to bring an argument about the fabric of clothing as an indicator of frumkeit level (aside from shaatnez, of course)that would be silly. the reason why this is even a discussion is because the association and affiliation of jeans (i personally think skirts are different here than pants, but thats my own opinion, others might disagree)is what concerns some in the yeshiva world. “yeshivish” people associate with the black and white “penguin” look crowd–its not that wearing that uniform makes them more frum, but it definitely provides affiliation. someone who identifies as yeshivish, yet wears jeans, is making a statement. its not a problem with the jeans; people just need to understand that they are choosing to deviate from what is considred normal by yeshivish standards.
also, i think some people will say that jeans is not a refined look, so they try to stay away. meaning, most “chashuv” rabbonim would not wear jeans, even when doing physical labor. if someone chooses to wear jeans from the practical standpoint (as wolf claims) that is also fine, but they just need to realize that they may look to others as wearing a more casual, coarse look than may be accepted by the yeshivish crowd.
its all a matter of affiliation. its not inherently wrong. the association that comes with it is what is confusing to some.