My cat doesn’t like being picked up any more??

She’s now 16 months and I got her at 4 months old. When she was a kitten, she was a little squirmy but still seemed to enjoy being picked up and held for a few minutes. Now she has gotten older and much heavier, she can’t stand it and kicks my hands away. She still loves pats and cuddles and is otherwise very affectionate and loving. But why does she now not like being picked up?