Well, I think I already pointed this out with someone else, but I don't remember who. It's about the US Army, US Marshal and Bureau Uniforms from the first Redemption. Why is Jack the only one who can wear them?
The US Army Uniform cannot be worn by John because the last of the six requirements in order to get it, the “US Army scrap” (purchasable from the Tailor in Blackwater), can only be acquired after the mission "The Last Enemy That Shall Be Destroyed", in which John dies. Therefore, only Jack can buy the scrap and thus wear the outfit. However, the US Army uniform can be worn by John in Undead Nightmare.
The US Marshal Uniform is unlocked by clearing all New Austin gang hideouts within 24 hours of in-game time. For some reason, this can only be done as Jack.
The Bureau Uniform is unlocked by achieving 100% completion. Because the player may only use John before the mission "The Last Enemy That Shall Be Destroyed", the player cannot have achieved 100% completion while using John and, as a result, the outfit can only be worn by Jack.
It does answer my question, but doesn't Jack hate the army and the government for killing John in "The Last Enemy That Shall Be Destroyed"? Something's wrong here. John should be able to wear them as well.
As to why this is, my opinion is that it is done to give the player an incentive to keep playing the game while they are using Jack. With the promise of new outfits (obtainable by continuing to play the game, such as speedrunning gang hideouts in the case of the Marshal uniform and achieving 100% completion for the Bureau uniform), it keeps players occupied and gives them more reasons to continue playing. Regardless of whether this is “realistic” or “right”, I believe that this, from Rockstar’s point of view, is the reason why these outfits are only available for Jack.