While I am all for the free market, making disposable battery companies label the estimated MAH on batteries would be a win-win in so many ways. For consumers, the environment, waste management, etc...
The alkaline discharge curve slopes dramatically, so those batteries provide dramatically different voltage when new vs used. Devices may or many not work at lower voltages so any battery life is difficult to estimate.
Rechargeables provide a very flat discharge curve, providing mostly the same voltage, so the steep drop off clearly signals the battery life end.