I too experienced an unwelcoming group in a guild I joined in Arizona. I hesitated joining another but six months ago jumped into one here in our little town where we live now. Some ladies have been friendly then there is a clique of about a dozen or so of them that I've observed that may have known each other a long time I assume...maybe they are founding members???
I wonder if it has more to do with the fact that we are mostly women who quilt? It reminds me of high school cliques, you're either in or you are out. I surmise that is why this Quilt Board is soooooo very successful, I've yet to post a question that isn't answered many times over, encouragement abounds, this is a wonderful 'guild' of quilters, men and women alike here.
I remember advice my very outgoing (never-met-a-stranger-type personality) FIL gave me years ago, "Get the other person to start talking about themselves, and there will never be a lack of conversation", ask them the most inane question that relates to them and very few people find it uncomfortable to expound on their 'expertise'.....I've found that to be so true.
If a person isn't naturally outgoing and effusive joining a new group and being the new kid on the block can be intimidating.