As others have said, making a block function account wide would enable account level information (which is something CCP is moving directly away from giving). Beyond this there are some problems with the block function in that there are ways around it, most notably corp apps.
Also, any mass-report -> mute function would be abused by literally anyone with multiple accounts or a group of friends. Better backend spam/bot detection would be the best solution but I’m not of the opinion that it’s anywhere near the top of the backend priority list.