It's not always about the average. This is not meant to be personal, but in general why some people have a hard time being picked up on a team. Two of the big ones are attitude and commitment.
Attitude, a bowler is either too serious or not serious enough to fit the team's expectations. Commitment to being there every week, paying league fees weekly, being there when it is your turn to bowl and giving 100% on every shot. I am sure there are also some teams who do not want a bowler because they know he/she will not sandbag and the team requires that for membership on their team

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Average based decisions are either the average does not fit with the rest of the team to stay within the cap. It could also not be high enough if the other bowlers are very low, putting them too far below the cap.
The other possibility is you are new and the other bowlers just plain do not know you well enough. Some teams just stay together forever and some leagues are tough to break into without having a full team of your own.
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USBC Bronze Coach "I cannot change the direction of the wind but I can adjust my sails to reach my destination." Jimmy Dean
Quaker 10/93 - 4/07
Quaker