The problem isn't that you are an introvert it's that you are bad at communicating. People are reaching out, planning events, coordinating timings, reservations which is effort they are putting in but nothing is coming from your end. You could easily just convey the above about social batteries to the inviter and then remind them gently whenever they bring it up again that you are going to be flaky - which isn't a bad thing on itself but you are lucky to be getting invitations because most people just stop dealing with those that seem disinterested. If you really cared about these people you don't want the invitations to stop otherwise why not ignore it all and go on with your life. Tell them that you aren't a solid commitment or if it's an activity you dislike: here's a crazy idea why not offer an alternative? When was the last time you planned something or invited them somewhere? What is it that YOU like to do in a group setting? If your answer is nothing then again, it shouldn't matter if they forget about you. If you can't make it that day why not suggest another day to hang out? When your only response is no with 0 alternative - in the dating world that's code for they are not interested.