Because nobody is interested in TF anymore, that’s why. There are many lists of improvement suggestions. Do you think devs will ever implement it? No, they don’t event comment on this topics. The modders are not assumed to fix the game instead of the devs. For example there was (and still is) a suggestion (since the very beginning) to make the tracks possible to cross each other (x-junction, diamond crossing), no big deal I would say, but either devs are lazy as fuck or coding amateurs.
It is such a pity, this game would have such great potential. I somehow love it, but all the flaws and unimplemented things make me sad…
But Cities: Skylines are out now 🙂