Probably to mask the scandals that President Chen is in currently, but such an exercise could be useful as practice and to show the PRC that Taiwan can fight.
The Patriot missiles won;t be able to keep up with shower of missiles raining down on them.
By the time Chinese forces attempt a landing, Taiwan will be a cratered mess.
I want some of what you're smoking. Just kidding. You're right about the sh*tpot Chen and his DPP cronies are in; but Taiwan would be lucky if 25%> could be depended upon to actually fight a PRC (Mainland) invasion.