Can somebody please explain why cash is not paying out until player dies on leaderboard?

If you notice your ends

			end
		end)
	end)
end)

The while loop is inside of the Died event listener!

You should move the loop inside of the PlayerAdded event listener.

The code is not indented well, and this could be why it is hard to see the issue.

game.Players.PlayerAdded:Connect(function(plr)

    local stats = Instance.new("Folder")
    stats.Name = "leaderstats"
    stats.Parent= plr 

    local kills = Instance.new("IntValue")
    kills.Name = "Kills"
    kills.Parent = stats 

    local deaths = Instance.new("IntValue")
    deaths.Name = "Deaths"
    deaths.Parent = stats 

    local cash = Instance.new("IntValue") -- # this is cash! not score
    cash.Name = "Cash" 
    cash.Parent = stats
    cash.Value = 1

    plr.CharacterAdded:Connect(function(char)
        local humanoid = char:WaitForChild("Humanoid") -- # Do not loop wait until something exists.

        humanoid.Died:Connect(function()
            deaths.Value = deaths.Value + 1
            local tag = humanoid:FindFirstChild("creator")

            if tag then
                local killer = tag.Value

                if killer then
                    killer.leaderstats.Kills.Value = killer.leaderstats.Kills.Value + 1
                end
            end
        end)
    end)

    while true do -- # in the PlayerAdded event listener
        wait(5)
        cash.Value = cash.Value + 3
    end
end)