Why am I not strong?

Hello to you and thank you kindly for reading this. I am a bit worried about my physical strenght: I feel that my arms are weak and it seems that I can't get any improvements in terms of strenght (I do have notice aesthetic ones, though). I've been doing Fitness Blender consistently for seven months, but I've always had a pretty active lifestyle; so how come I can't beat my 67-years old mother at arm wrestling? Even my sister (which always had a very sedentary lifestyle) is stronger than me at pulling up heavy weights! I know that we shouldn't compare to others and instead focus on our own strenght, but come on, it seems like a joke. Why am I sweating, huffing and puffing every day if I cannot become strong?

Sorry for the whinge, but I'm a little disappointed about myself...