PieFed is a link aggregator. Mastodon is a texting platform. They are different paradigms. While they both use ActivityPub to share information, they do not each mirror the core functions of the other.

It would be like asking Mobilizon, the ActivityPub events manager, to also support texting and communities. It wouldn't make sense. Its core function is scheduling and managing events. It uses ActivityPub so people can see event information and updates in their Mastodon account, but people can't schedule or change events from Mastodon.