system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does practically every website still have trouble handling high traffic volumes even when they're expecting it?

It seems like everytime I go somewhere to buy tickets, watch an event stream, etc. the site hosting the sale/stream/etc. crashes. How is this still the case in 2016? Can they not prepare servers for increased volume ahead of time?

EDIT: Thank you everybody for your explanations, I guess the technology just isn't there yet. Still incredibly frustrating though!
gpt
Servers have a finite amount of processing power. The only way to increase your capacity is to get MORE servers or upgrade the hardware of existing servers. This is an expensive proposition and takes work to do. It doesn't make much sense unless you're expecting to have to handle this sort of volume a lot.