What exactly dont you buy about there not being enough drinks for the inbound flight?
Its simple mathematics. If 354 passengers (45-49 premium) drank what they liked during a flight, there isn't enough space to keep more for the way home.
Do you think the crew did it on purpose to make your flight awful? Did you go to the galley and ask for extra drinks? Because you can you know, they don't bite.
MikeBravo was correct with the effects of alcohol being 3 times as much as on the ground, and it is completely illegal to be drunk in the air, ttherefore the crew were being very cautious I imagine.
The free bar is not the only perk for premium passengers. Its a nicety, not a necessity. Now don't get me wrong, im as generous as the next with the onboard bar, but I don't understand the need to have 3 g&t's all at once, instead of just waiting for the next drinks to come through.
Plus you do get free pouring wine with the meal, so that's 4 drinks services, much more than on certain scheduled airlines I can assure you.