Modern product development is highly cross-functional.
A single user story (or “work item”) can have many people involved — each assuming a variety of hats. Sometimes work happens individually (serially and in parallel), sometimes it happens in pairs, and sometimes the whole team works together at the same time (e.g. mob programming).
Yet…many tools require a single person to be “assigned” to the work item. At any given time, the work only shows up on a single person’s “dashboard”. There can only be one current assignee.
Stepping back, let us acknowledge that there are a number of viable management (and collaboration) philosophies out there in the world. Some believe strongly that if “everyone is responsible, no one is responsible”. Others are advocates of “joint ownership”. Some teams are big advocates of individual responsibility. Other teams take a more collectivist approach.
The problem is that a number of popular tools are biased to one philosophy (the “single wring-able neck” one). What if you have a tester, UX, and developer wanting to jointly own the completion of a user story? And they want to swarm/pair? Many tools cannot represent this without needless sub-tasking, custom fields, etc.
Sure, you can just disregard the tool (and many do). But that’s a drag.
Some products are opinionated. They enforce a “way”. When you buy that product, you accept the way. This is fine when there is a “way”. Collaboration tools, in my humble opinion, should be more agnostic.