When everyone is responsible for an account, follow-ups wait for someone else to go first. A single named owner does not mean a single person does the work — it means one person makes sure it happens.
Separate the owner from the team
Give each account one primary owner and list supporting roles separately: technical contact, executive sponsor, billing contact. The owner coordinates; the roles contribute.
Use simple rules to assign new owners — by region, segment or account size — so assignment does not depend on who happened to see the record first.
Ownership is not who does the work. It is who notices when the work has stopped.
Plan for change
People change roles and go on leave. Agree a standard handover note and a short overlap period so that ownership changes are recorded rather than improvised.
Once a quarter, list accounts with no owner or an inactive owner. It is usually a short list, and fixing it is one of the most valuable hours a team can spend.