The IL was created for long-term injuries, being a keeper league. You don't want to lose one roster position for the year if one of your definite keepers goes down. 6 weeks, 2 months and greater, especially season-ending, not for relatively minor 2-4 week injuries, such as ankle sprains or hamstring.
The 5 consecutive games rules is very simple to follow, and can be monitored easily. At the moment, that's the only condition for someone to be put on the IL. It was placed because sometimes, Player A can be injured and the team says he is out '1 month', and he returns in one month. All is good, so why do we need the 5 games? Because another player, Player B can be out injured '1 week', but it drags onto a month. At the end of the day, they are both out 1 month, and that's the important thing. And Player B wouldn't have had the IL advantage...
So, The other argument to come up was, if Player C injures his ACL (or another serious injury), why does he still has to wait the 5 games before being put on IL. So there was a thought that you could allow a player to be put directly up to the IL after missing at least one game, but then he has to stay there for at least 2 months. Even if he comes back earlier, you must keep him on there.
I don't mind allowing the 2nd rule also, but it just makes things a little more complicated, so I prefer it to be much more simple. But it's definitely an option.