why can't we go back to the old shareware system?
Because unfortunately for all of us that loathe the free + in-app micropayment model, it actually makes money. There's no way an entire ecosystem built around this model would have sprung up if everyone hated it as much as I did.
There are many, many people who download and play a huge number of free games, and never bother paying, or perhaps pay for a game rarely. Many of those people (like kids) are time rich and cash poor, so don't blink as spending ridiculous hours grinding away. There are a much smaller number of people who get addicted to these games and spend a ridiculous amount of money on in-app purchases... far more than would have ever been paid if they had just purchased the game outright. Those people are the real targets.
My only hope is that people eventually grow tired of these sleazy tactics and refuse to participate. Then again, people still waste money at casinos and buying lottery tickets, so I'm not really holding my breath. I'll just continue supporting developers that sell their games up-front for a fixed price - a model I much prefer.