Why do celebrities or people celebrate their sobriety?

I’m someone that doesn’t drink very often, and if i do i only drink socially. I keep seeing instagram posts or twitter posts of people celebrating being like “10 months sober” or “1 year sober”. I understand the difficulty and disease that is addiction but what i don’t understand is why some celebrities with no known alcohol abuse problems or issues at all posting about their sobriety. like is sobriety completely abstaining from drinking at all, even socially (because these people are the kind that only seem to drink socially)?? and is it that difficult to abstain from drinking??