Discarding them outright is a bit excessive, but it's actually very common for managers to de-prioritize resumes with excessive job hopping. Either that, or to craft back-loaded compensation packages that encourage longer tenures.
A few short jobs is not a problem, but when someone has a resume full of 12-month jobs and constant churn it's not a good sign. If you do have to hire a job hopper, you have to be careful to not put them on critical tasks or anything long-term because it's not like they're going to suddenly decide to stay at your company for 4 years when they couldn't do it anywhere else. It's not a mystery.
A few short jobs is not a problem, but when someone has a resume full of 12-month jobs and constant churn it's not a good sign. If you do have to hire a job hopper, you have to be careful to not put them on critical tasks or anything long-term because it's not like they're going to suddenly decide to stay at your company for 4 years when they couldn't do it anywhere else. It's not a mystery.