Batter was overmixed.
Batter had too much liquid or fat.
There was too little or too much leavening.
Bread was underbaked.
Batter stood too long before baking.
Batter had too much sugar.
Batter had too much leavener.
Bread was still warm. Cool completely before slicing.
Batter was too thin to hold the fruit, nuts or chips. Next time, chop them smaller or use miniature chocolate chips.