It's not about programming, I think it would be super easy to add additional code,
it's about balance in the game,
it would need to test the changes properly and thoroughly to check if the gameplay balance is violated with adding new tribes,
and that takes a lot of time and resources,
and it would be too much of an effort for this game.
hmm I dont know.. They could start test servers that run simultaneously to the normal worlds but with the new tribes implemented. There they could be tested with help of the community and once they feel balanced, they can be released onto the normal servers. TK already had test servers for new features and balancing the new tribes cant be too hard since every tribe has 10 kinds of troops (well 8 that need balancing because chief and settlers dont really need balancing) and every troop has 5 stats (plus crop consumption which isnt too hard to think about) and resources. The developers should have enough experience to instantly roughly know the right stats so its kinda balanced from start and the details like 5 attack more/less can be worked out through test servers and community feedback.
Here is obviously a large community ready and waiting for new tribes, so they are eager to help and give feedback. I know I am
And lack of ideas for new tribes/troops is really not a problem. Im on this forum for roughly a week now and Ive seen many great ideas that I would like to see implemented right now regarding new tribes. And even more genereal ideas, but this is the wrong thread for that.