There's a finite amount of resources for the development team to add new features to the game. Franchise Co-op is a request I've seen in the last few months come up more often. I didn't see it too often for Madden 19 on the forums though. Couch Co-op in general is always a fan loved feature, but with a significant portion of players going to online modes from their own consoles, couch co-op style features aren't as popularly vocalized as they used to be in the past.
Some examples of factors to consider are demand for the feature from the community, how hard and long it would take to implement, along with the costs involved. If it's difficult to implement and only 2% of the playerbase will frequently use it (just throwing out hypothetical numbers here), they may have to put it aside for other features higher in demand, despite it would be pretty cool to have. We see a ton of awesome suggestions every day and when the team has hundreds to choose from, there's difficult decisions to be made on what makes it in and what doesn't.
The great thing about these forums though is that we can discuss great features like this and gauge how many others out there are interested. I'll frequently merge some posts together here to help vocalize requests when I can. If anyone like yourself is interested in this type of mode, feel free to jump in and join the discussion. We can't always promise features will be implemented in the current Madden or future iteration, or if at all, but we're always open ears and willing to chat about what could make the game a better experience for you.
Thanks for coming by with your feedback, @Gabebanks3333