1. Takes a LOT of time.
2. To develop you need to donate. But, because The game is international, so there are no separate national servers or cities. In most cities, everything was captured and held by Asians (mostly the Japanese, then the Chinese and Koreans). And no matter how much money you invest, you won’t beat them. Because what 5$ or 50$ means to us (especially now!) is not at all what it means to them! Investing even $500 a month, you will be just a makiwara for them, without any chance of even a response!
3. In order to somehow protect yourself from the constant attacks of Asian surfer donors, it is necessary to constantly put up shields to protect the base. You have to buy by spending in-game gold. And constantly waste your nerves, worrying during the day at work, in the evenings on the way home, jumping up in the middle of the night, fearing that you won’t have time to install a new shield in time. And they will burn you, you will lose the troops you have been collecting for so long, your rating will drop significantly and you will have to invest even more money to heal whoever is possible from the army and train new soldiers. And the rating will remain in the same range, because they will constantly lower it for you.
So the choice is small, or be a makiwara and a source of supplies for the enemies. Or, if you are ready to sponsor developers coolly, invest tens of thousands of dollars, become super cool and bend everyone over.