It’s not that hard to fathom. Literally tens of millions of people know the name Grumpy Cat. Maybe 1% of that number know about Grenade Beverage.
Grumpy Cat is a big enough phenomenon that they could probably make back the fee just on purchases like that. Let alone people who would actually drink the stuff.
For those that are interested, it's alright, but not my favourite. I'd recommend trying it if you get a chance.
I thought the name was something to do with Mikhail Gorbachev, but it isn't - the brand has been produced in Berlin since 1921 after its founder Leo Gorbatschow left Russia during the October Revolution (thanks, wikipedia).
Fairly decent vodka for the price though; would drink again, but since Stolichnaya and bisongrass vodka are also much cheaper in Germany than the UK they're a better candidate for limited luggage space.