Just my personal reasons:
It depends on what you mean by in.
I love agility but I hate trials. It is something my dog and I do. We don't need anyone else.
I have a full-size agility area 100 feet from my front door. If you drive past my home, you would classify me as in agility.
I don't like getting up in the morning and driving 30 to 60 miles to go to a trial (I know that's not far for many, but it is for me).
I don't need someone to travel a 1,000 miles to tell me that we missed a contact or dropped a bar.
A trial will take an average of 12 hours for one to three minutes of activity. I can sleep in and still set up six courses on a Saturday or Sunday and get a lot of other things done between runs.
I don't seek social interaction. It is another contradiction in my life. I enjoy interacting with people at work but not otherwise.
I see absolute no value in titles and awards.
I do not like being outside in less than ideal weather conditions.
At one time I was doing about two, 1 day trials a month. I have now greatly reduced that. I have done two, one day trials this year and only have one more planned. But I still consider myself in agility. I have upgraded my equipment. We do agility almost every day. I have three informal students who come over once a week and I help them. I have went to watch the AKC World Team tryouts two of the last three years. I consider myself in agility but if someone counts the men at trials they will probably not find me.
Bill Fehn
MN