Why are load resistor values in common-emitter amplifiers so large?
Common-emitter amplifiers are mainly used as voltage amplifiers. If you need a lot of power, you can feed your output into a power amplifier, such as a common-collector amplifier (emitter follower). A CC amp has a high input impedance, a low output impedance, and a voltage gain near 1. The current gain depends on the load, and can be much greater than 1.

There are several different power amplifier topologies commonly used for driving loudspeakers. Look up "class A", "class B", and "class AB" for more information.