That's how the bats find their way in, air flow.
I would wonder about all the trouble of putting a large piece of tubing in, when there isn't any real need. Maybe one could just run it in and epoxy plug the hole where the wire comes out. There is this perfectly good tube for the wire to run through, so we provide a seperate tube for it to run through? Not really seeing that. Chafe, water, and easier repair are certainly thoughts. Just not convinced it is a reasonable response to that stuff.
OK, so having rejected the crazy, here is another one just for fun. A lot of the problems go away if you get rid of the seatpost, and there can be payoffs for brakes, or maybe gear hubs. The simple method is to have a seat boom. Another option is to have, something else, there are other ways of mounting seats... So back to the boom. I want some seat post, just not so much that it cuts my wires or cable. Main issue I see is getting the thing packed with a honkin boom on it. But that is how the Bike Fridays, roll, so it can be done. And that isn't a problem for everyone, some people bike tour without chugging down a pile of av gas before they get to the starting line.