People leaving early is something that's been happening forever. The sad thing is the reason. Most supporters that leave early only have one reason: Get home 30 minutes earlier.
It's entirely their own choice, but it's such a pathetic thing to watch, as someone that does stay until the end. You can't punish it, cause you can't exactly tell them to bring proof that they have a valid reason... like a doctor's note haha. Or keep the place locked down, like a prison. It's up to them. If beating the traffic is more important than supporting the team, there's very little you can do.
I always kinda hope that somehow, one day, they feel a bit of shame and they realise the team needs their support. Especially in those final minutes, when the players are tired and things are perhaps difficult or not going well.
Whatever they do, I will always be there when that final whistle goes. After all, we pay enough for it, might as well enjoy it ;)