There are two major factors in what killed the funny animal market in the US.
The first and simplest is TV.The comics existed as away to promote these characters in a time where home video viewing wouldn't be an option. By the 70s, kids could watch these cartoons on TV at home. Not all the same funny animals, but it hit a similar niche,
The more complicated answer is Dell/Gold Key dying with the downturn in the comic market in the late 70s. And that happened with the slow death of newstand distribution. A lot of people seem to wonder why floppy comics are only sold in comic shops for the most part- this wasn't a random choice done to chase away normies, but due to the fact that newstands increasingly wanted less to do with comics- they were cheap and thus made little profit,
Newstands pushed for one of the worst decisions that would forever impact the market- they made publishers charge more. It wasn't an unreasonable price increase , but it was enough to begin to price kids out of the market. It also lead to the emergence of comic shops, since newstands would carry less variety of comics(as well as becoming less common place over time)
Gold Key eventually died when it couldn't find a way to distribute the comics decently anymore- basically killing a legacy from Dell where Disney licensed comics used to be the biggest in America, even into the 60's.
So you had an industry that basically left kids behind and never really tried to get them back, and priced them out entirely.