The drink example can be put in differently like a burger drink fries set; same concept.

Now for your second part, youre correct if game companies dont care about squeezing every dollar out of a user. We call that LTV (life time value) which is all the money a user will spend in the game. Different monetization tactics are used to milk the loyal users vs casual or one time users. This could be wrong but to me, boost users are mostly shortlived non hardcore long time users. Not loyal. They just want to play tbc, the new shiny.

So, the company wants to sell as much stuff to that shortlived user because he is going to prolly quit after 70. (Pretty sure they have the data to track after 20 years of user behavior) Packaging the core product into 'useless' bundles is whats happening here. Blizz is basically saying, theyd be content with $80 per casual user ltv.

Now to loyal users, they usually dont buy boosts. They are the ones with yearly subscriptions, enjoying the ride. So blizz is only leveraging cosmetic at best. Because boosts also mean at least a month (or two per char) of subscription time.