What is a consequence of working in isolation on long-lived code branches?

According to the SAFe DevOps Practitioner 6.0 study guide and handbook, working in isolation on long-lived code branches can have negative consequences for the Continuous Delivery Pipeline. This includes making the trunk/main branch less stable and more prone to conflicts and errors. The handbook states that "Working in isolation on long-lived code branches can make the trunk/main branch less stable and more prone to conflicts and errors."1 Therefore, it is recommended to use short-lived feature branches and merge them frequently into the trunk/main branch.