If you can (and if you're not afraid of dogs), get a dog.
If you can't get a dog, try to find a way to incorporate a dog in your walk. Either through an app or sometimes the dog shelter sets up a volunteer squad to walk the dogs, or some other solution I don't know about.
Walking used to be a chore. Now it's something to look forward to and to remember afterwards.
No offense intended here, I promise, but suggesting somebody take on the enormous responsibility and life alterations of dog ownership just for the benefit of making walks more palatable seems full-blown ludicrous to me.
hm? cats need exercise too, if anything it's way more annoying because you have to either take them on walks where the cat spends half the time walking in a circle, and half the time wanting to sprint at full speed, or you have to get cat toys and make them run around for half an hour straight.
Just letting the cats go outdoors on their own is a bad idea for the same reason that doing so with dogs is a bad idea, they'll kill a tons of animals in the wild and will likely get hurt or even killed.
Especially in a world where most places have vehicles zooming along without a care in the world, it's extremely irresponsible to have outdoor cats.