Touhou is a game of resource management practically by definition. =V
Yes, but HrTP, SoEW, PoDD, LLS, MS, EoSD, PCB, IN, PoFV, MoF and SA gives you all your resources automatically. You don't have to work for them.
That means that UFO makes resource management much more difficult. Not only can UFO's easily change their colors just before you grab them, they can retreat into a huge cloud of bullets, they can leave the screen etc.
And everytime they do that, you lose much needed resources.