Actually, even though I can't account for all my flights in business class, I would say that on about half or more of these flights I was served the drink right after boarding and stowing my carry-on. Now I have to also admit, that on many occasions I boarded towards the end of the boarding process, so I guess the other business class passengers had already gotten their drinks, but I certainly remember boarding among the very first too (mostly pre-pandemic, since I think pre-departure drinks came back just during this year and this year I've only boarded late) and still getting my drink amidst passengers blocking the aisle (I guess booking the 1st row helps a bit in that respect).

But yeah, I've also had flights, where the drinks were served after leaving the gate and the FA's were so quick to collect the empty glasses, that a few of them stayed with the passengers, because they weren't done yet, we've even had a couple of occasions, where they never collected these still not empty glasses until after departure and initial climb, so I guess they are quite preoccupied with their other duties...

Anyway, the glasses containing water or juice are always quite full (though that's arguably still a long way from satisfying one's thirst), but the quantity shown here looks like that glass got just the last few drops left in the bottle ​​​​​​.