system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do big companies like McDonald's, Coke, Geico, etc. spend so much on advertising when they are already universally known?

I see commercials for Coke and Mcd's all the time (new ones, not repeat ones), and I can't help but wonder why they bother.  I mean, why spend so much money on an advertising campaign when practically everyone knows about your product and everyone universally buys it?

Same thing with PR campaigns for these big companies, what's their incentive?  Why do these big companies keep pumping out new ads?
gpt
Market share.

Everyone knows about McDonalds and Coke, but if they don't stay at the front of your mind their competitors will start to erode their market share.

All the other players in those markets advertise heavily, if the market leaders don't some of the less devoted consumers may drift off to their competitors.