I read an article last week that GSK is focusing on certain "power brands", that is their sensodyne toothpaste, some antiinflammatory brand, and so on. Horlicks has taken a massive backseat in their portfolio due to room for growth. I think Horlicks may only be available in India where the factory is.
It's quite a turn around for the Horlicks brand which they remarketed in 2014/2015.
My grandmother is a 5 decade Horlicks addict, she's now switched to Ensure.
Ps, I have one unopened Horlicks left (I usually buy bulk of certain products), at least I still have 12kg of unopened original Milo.