If you ever wondered why people ship Sonadow- read this.
I see people be confused about the why's of Sonadow. Why do people like it? Do you seriously ship it? You've seen the same things and you've watched the cutscenes and damn it all it just doesn't make any sense. Maybe you've read comments from people insisting that xyz interaction between Sonic and Shadow means they must like each other and you saw the comic panel where Shadow is carrying Sonic and it doesn't mean anything to you, and you handwave any explanations off because you don't see how anything in the canon means they want to date. Perhaps you've perused the relationships tag on Ao3 and saw that Sonadow is by far the most written-about ship in the Sonic the Hedgehog fandom. So why? Why???? Someone tell me why!!!!
If you want to know let's get cooking fellas.
1). LGBT ships are king.
Historically shipping and fanfic served as a way for LGBT people to get representation from media that uh, didn't want to do that. This has been true for decades, it's tradition and so deeply engrained into fandom culture that there's no two ways about it. The people writing fanfic tend to be female, queer, autistic, and any other sort of 'othering' you can think of. Gay ships are always more popular, and usually, M/M ships are more popular than F/F ships unless you're Madoka Magica or otherwise your cast is full of women, which Sonic is not. The boys usually get the spotlight, and you can argue that characters like Amy and Blaze kind of don't even really know each other. Do they ever hang out in the games? Are you going to claim that Rouge and Blaze are a viable ship? Can you be so fucking serious with me. It's about the boys.
2) Enemies to lovers
People LOVE LOVE LOVE LOVE enemies to lovers. Currently, on Ao3 there are 165,000+ written works that are enemies to lovers. It's an extremely popular trope that's a tale as old as time. Does anyone hear pride and prejudice?
3) Teenage girls really love Shadow.
This one is self-explanatory. I feel like I don't need to explain what would happen if Shadow were a human and not a hedgehog. People are thirsty for him as is. I suspect in some ways the obsession with Sonadow from some people is a desire to 'fix' and support Shadow in ways he isn't in canon (i.e. romance, opening up, talking about feelings, etc.) and they use Sonic to do that. I'm not a teenage girl and I write fanfic, but I would be remiss to not speak on the fact that uh, yeah they're the ones usually doing that lol.
4) Shadow is perfect fanfiction bait.
-broody
-dark past
-doesn't talk about feelings
-traumatized in some way
-cool
Fanfic tends to center around the more 'complicated' characters in media, especially characters as popular as Shadow. If you read fanfic this is just something you can intuit. Shadow feels ripe for fanfic picking.
5) Sonic and Shadow are perfect opposites
This one is also self-explanatory, but fandoms tend to love pairings where there's the "dark and gloomy" one and the "sunshine" one. There's kind of no one gloomier than Shadow and no one sunnier than Sonic. They're the perfect odd couple.
Tl;dr: Sonic and Shadow are the perfect gay enemies to lovers odd couple for people online to get obsessed over. It's a lot of popular tropes shoved together in a delicious stew that can be reheated and served over and over again. Eat up! Do it! Embrace Sonadow!