The magisterium teaches, and the people accept.
It is perfectly good and right for the laity to make their concerns known to the hierarchy and the magisterium. However, truth does not “bubble up” from the laity. The pope and bishops do not canvass the laity, they do not say “let’s see how the laity are thinking these days, and if there’s something that’s not to their liking, let’s take a closer look at it, because after all, X million Catholics can’t be wrong”. If it were something on which everyone in the Catholic Church, or pretty much everyone, were agreed upon, and had always agreed upon, then yes, that would carry a lot of weight — we have assurance that the whole Church can never fall into error, otherwise the gates of hell would have prevailed.
I think we all know the “big issues” on which large numbers of people, in this part of the Church or that — as opposed to the whole Church throughout the world, in its entirety — dissent or disagree. They are issues that relate to marriage and sexuality — contraception, premarital sex of all types, divorce and remarriage without benefit of annulment, homosexual activity, and to some extent abortion. Being able to stand back and objectively assess the proper and ordered use of one’s sexuality, and to accept the consequences of that, is not exactly the human race’s strong suit. Human nature is notoriously weak in this regard — some speculate that the original sin of Adam and Eve was a sexual sin, and that the fruit mentioned in the Bible is just a metaphor — and when you have the larger society begging and pleading for greater license in these matters, it’s very hard for Catholics to resist this siren call. Some don’t even bother resisting.
“Nobody believes that there’s anything wrong with X anymore, why can’t we do X like everyone else?”. That’s not being objective or seeking truth. That’s not “conscience”. That’s just wanting to have fun like everyone else gets to do. And then for these people to say “our conscience doesn’t tell us that’s wrong”?
Of course it’s not going to! When you hear it constantly from all quarters, when ostensibly “good, religious people” of other faiths aren’t troubled by it, when the media brainwashes everyone, when doing this or that is presented as being cool, or hip, or enlightened, or progressive, or “up with the times”, no, you’re not going to think that anything’s wrong with it. The secular and non-Catholic world, in a very real way, becomes our magisterium.