rarely will you see the same ad repeated everywhere

I rarely ever watch cable but I swear cable ads would repeat the same exact video ad multiple times per show but maybe it has changed nowadays.

Why is it that way? Is it really more profitable,

Probably depends on the product. For google search where your search query is generally highly relevant to what you are looking for and therefore advertisers, probably not much. For facebook when I am scrolling through the news feed and I'm not looking for any product in particular, probably a lot because that is the difference between showing me a generic ad with low click through rates versus one that is tailored towards things I probably want and therefore much more likely that I will click on it.