There are so many animals out there that want nothing more than to love and be loved in return. It hurts so much when they leave us (one of the downsides of having a longer life expectancy than them I guess) but what keeps me going is the knowledge that I've made the world a better place by giving a great life to at least a few of them in our time here. We all have to share it, ultimately.
Pets make our lives richer, fuller and (for me at least) bring balance and happiness to it. I'm one of those types who has a VERY hard time liking, getting along with or trusting people easily. Usually I expect them to be shallow, phony, manipulative, inconsiderate or what I call "SOS" (Stuck On 'Stupid'). Either that or they're just looking for some way to screw me over. Some folks (the rare ones) prove me wrong and ultimately gain my acceptance. Most don't and just reinforce my "default" belief that people typically just suck and are something best left avoided. OTOH, pets are never selfish or inconsiderate - they only want attention and love and to play and be happy - and to bring the same to us (well, occasionally they obsess about food too. . .)

They're always honest and true to what they are. Point is they bring me a lot of happiness and give me a certain amount of balance in my life.
It's too easy to become grouchy/negative when surrounded by a-hole people all day. Animals go a long way to offsetting that. They're all awesome and give such happiness to my life. I'd probably have gone crazy or turned into a total antisocial grouch a long time ago (worse than I probably am already) if not for them. . . They literally keep me going some days.
Here's Charlie (my much beloved cat who passed away from cardiomyopathy back in January), and his surviving companion Bonnie. Linus & Lucy (the two black & white ones) came later.
Charlie (R.I.P., please know you are and always will be missed)
Bonnie (a.k.a. "Fuzzy")
Linus (total scamp, blue collar) & Lucy (the mellow one - Linus' mom, pink collar):