And why it's a massive can of worms.
Here I'm going to list all the problems I have with roles that interact with the Graveyard and dead players (I'm going to just call the GY Roles from here forward).
People hate slowrolling games already. If you could check the faster timer button in ranked, people would. If GY Roles get added, you would be forced to wait out every single game until its conclusion. In fact, I would imagine you would get a gamethrowing vio or sui vio for leaving a game (while dead) before it's over.
One of the most popular games at the moment is Fortnite (and it's predecessor PUBG). When you die in this game, maybe you stick around and watch the guy that killed you for a minute, but then you can join the next game right away and try to win again. I don't know about you guys, but I think most players on EM are equally impatient and would rather join the next game right away. There wouldn't even be anything to watch because the spectating graveyard that we know now would have to be changed so the dead couldn't see what PR everyone is.
You'll also be forced to wait around in a game even if there's little to no chance that a GY role will bother with you. Two of the most suggest GY roles are resurrectionist / necromancer or medium. The former lets you revive players, the latter talk to the dead. GY Roles will always want to deal with a PR. If you're a blue in a setup with these roles, you're going to be waiting around in the graveyard because you probably have nothing to offer a GY role.
Having a Mafia-aligned GY role would be very tricky indeed. A mafia sided resurrectionist wouldn't work for two reasons. It would keep the LYLO ratio as it was from the start of the game if a mafia was dead and if a mafia is revived, the town basically know who they are and will just kill them again. Obviously this is solved with no reveal setups but that's a niche and doesn't solve all the other problems.
Finally, I have to bring up one of the older points that's been made about changing the graveyard. It removes a learning experience from the game. As a new player, watching the game unfold while dead is a good way to see what is happening behind the scenes and helps you get better acquainted to the game. This is no substitute for a tutorial that this game lacks and I'm not suggesting new players are swarming in, but we would be removing what little help we have.
tl;dr
- people would be force to sit around in games after they die
- nilla roles will feel this the most
- very hard to balance GY roles
- removes the only learning experience EM really has