Since the 2020 release wave 1, the ability exists to filter the activities to be shown in the views:
- All activities
- My Activites
- My Open Activities
- ...
https://docs.microsoft.com/en-us/dynamics365/sales-professional/manage-activities#filter-the-list-of-activities
Since the customer won't use every activity, only a select part, the list is to long.
Even if the views are filtered for certain activity types the list keeps showing all available activities. (no, security is not an option on activities 😉)