Like if you take them for a walk, and then you also want to walk further for your own exercise, but the poor things are too old or disabled to keep up. Then you can put them in the stroller and push them along with you. I saw a variety of cat/dog strollers for sale online, and I'm just assuming that's why. Although the cat ones might be used so that the cat can be "outside" without running away. I don't know lol.
Caption this Meme 
