The TL;DR version of this post is:
The difference between Shory and Jeric is one is a pair of star crossed lovers and the other are friends-with-benefits who need to talk about their feelings.
The long version is:
You kind of... can't compare Shory and Jeric. But also, you have no choice but to compare them.
Jeric would not exist without Shory, that is just a fact, they exist to be a second Shory in a sense, so you would expect a lot of similarities between the two ships and, like, yeah there are. But these two ships are also so different.
@mangora explained it really well in this post, and I just want to delve deeper into that.
Shawn & Cory as both a friendship and a romantic pairing have something Jack & Eric don't: in-text depth.
By the time Jack shows up, we've watched four whole seasons of Shawn and Cory’s dynamic, and since Cory is the main character, many episodes revolve around him and Shawn. Not to mention (and this is a fun fact for you) Shawn and Cory are the only two characters who show up in every single episode. It's true! All 158 episodes have them. Not every episode has Mr. Feeny! Or Eric! Or Topanga! But every single episode has Shawn and Cory. (Here is my source, which I have checked myself on the BMW fanwiki.)
Four seasons of Shawn and Cory, that's 89 episodes. Jack shows up in the 90th episode, and even then there are still episodes he isn't in.
All of which is to say, the writers had more time to flesh out Shory's relationship.
But like... the writers still had a little under 70 episodes to flesh out Jack and Eric's relationship... and they kind of don't.
A lot of what makes Jack and Eric special is purely fanon.
I know I've just swung a bat at a beehive by saying that, and look! I love Jeric! I do genuinely believe they were built in a way that made them prime for canon ship status (were it not for the fact this show was made for American families in the 90's) BUT you have to admit that outside of the stuff that's clearly meant to be haha that's gay (sleep together, bathe together, and even get to see each other naked, etc) fans really had to fill in a lot of the blanks.
And I think the reason for this was because the writers could afford to give Shory a deeper relationship without it immediately coming across as gay, because Topanga was there.
They kind of did this with Rachel in S6, but it's obviously shallower, and she & Jack don't last.
Which is also why there are far more smutty Jeric fanfics than Shory fanfics, and why you see a lot of this formula in Jeric fics:
Eric offers Jack sex, after a lot of hesitation Jack accepts, they have sex, feelings are then discussed. They get together.
Whereas the formula in Shory fics usually goes one of two ways:
Topanga breaks up with Cory, sometimes because she realises he's in love with Shawn before Cory does or for some other reason. After some reflection, Cory accepts he's in love with Shawn, they get together.
OR
Shawn loves Cory. Shawn tells Cory. It's mutual. They get together. These fics either take place after Cory and Topanga break up or take place in an alternate timeline where C0rpanga never happens.
There's a reason why writers gravitate towards those narratives for those ships.
You could, in fact, write a fic where Shawn offers Cory sex, and those fics do exist! Just as fics where Rachel breaks up with Jack because she realises he loves Eric exist. But you're more likely to see it the other way around.
So why is that? Why is Jeric the (for lack of a better way of putting it) the friends-with-benefits to lovers ship? Well... because that's kind of how they're written in the show.
When you think about all the gay Shory jokes in the show VS the gay Jeric jokes in the show, you see a trend, and the trend is this:
Shawn & Cory toe the line of having an affair.
Jack & Eric are fucking.
Think 'An Affair To Forget'/'It's Not You... It's Me'/etc VS "[...] Girlfriends sleep together bathe together, and even get to see each other naked." "We already do that."
Jack & Eric in canon never really talk about their feelings. We see Shawn talk to Cory all the time and vice versa, but name a BMW episode where Jack and/or Eric really talk about their feelings. I think the closest we get is in S5 E2 when Eric encourages Jack to bond with Shawn.
So, says the fanfic writer, let's explore that. Let's explore Jeric growing closer through sexual intimacy, because the show sure as hell makes out they're sexually intimate.
And that makes sense because Shory grew up together whereas Jeric met at university. Shory's feelings have blossomed over years and Jeric are horny young adults.
Anyway if you've read this far: Hi!!! Remember what I said about Shawn & Cory always toeing the line of having an affair? Yeah, guess what Chapter Twelve of my fanfic is going to explore?
