just like everyone else said
it all boils down to balance issues. I don't mean "omgz my towers suxorz make it easier!" I mean a ton of little facts don't make sense. The only way I ever lost was by starvation. I had about 12 farms and 100 population when I realized something didn't add up. Starvation should be next to impossible with two or more farms. When the number get low, that means there are less people. less people eat less food, not more. In that sense, there should be a vast, unimaginable surplus of food when enough people starve off.
alos, the idea of each of the same buildings costing more than the last is played out and also just a cheap attempt at making the game impossible to beat.
try using logic, and youll have one of the best flash games ever.