we give each other gifts but we don't say thank you with each other

Tweet

One of my sister give each other gift expensive and valuable one, we like each gift we give each other. we appreciate each gifts like she gave me a beautiful popular brand of watch for my birthday and i usually give her precious stone jewelry what i have she have it too.. but never did i heard thank from each other.. my mom wonder why? but we usually say thank you to everyone we got favor as our parent taught us.