I’m kind of the oppisite in that I prefer Nostr over ActivityPub, but both have their merits. As for technical ways Activity Pub has a leg up:

• Comunities - Activity Pub is built around individual instances, with people able to join communities focused on their interests and/or that have their preferred moderation policies. Some software exists to do similar things on Nostr, but that’s not what most people use.
• Platforms - In a similar vein, Activity Pub is probably easier to make a platform out of, be it Meta making Threads or you making your own social media service for your friends. On Nostr people’s accounts exist outside of the infrastructure they use, so it’d be hard to provide a more unified experience.
• Ease of Use - Activity Pub generally has a lower technical barrier to entry, you can sign up with an email and a password on most servers. Outside of (upcoming) DiVine or using Frost Bunkers, there’s really no easy way to join Nostr without learning how to manage keys.
• Standardization - Acitivity Pub has existed for the better part of a decade, and the protocol hasn’t changed much for a while. Nostr is not only newer, but breaks it’s functionality into various NIPs (rules on how to interpret posts of specific types, e.g. shortform text, longform text, livestreams, etc) of which there’s 100+ official ones (and plenty of unnofocial ones).