Be the one who invites. Most people are waiting to be asked and assuming nobody wants them there.

Most people spend their social life waiting for a signal that they are wanted, and read the absence of an invitation as the answer. Everyone doing this at once produces a room full of people who would happily have come. The scarcity is not of willingness but of organizers.

Send the message for the thing you want to do instead of hoping it materializes. Keep it specific, with a day and a place, since vague plans die politely. Some people will decline, and that is the ordinary cost of being the one who asks.