The printer can be left on 24/7. Most printers will go into a stand-by mode where they consume very, VERY little electricity. If you actually turn the printer off, when you turn it back on again it will have a lengthy start-up time. Also, if it is a laser printer, you might have to wait for the toner to warm up for a lengthy period of time in order to be ready to print. Or you might have to wait for the printer to go through a conditioning cycle. The reason you can’t turn it off/on through Alexa is because no one wants to do that.
Plus, if you turn the printer off…how would you possibly be able to turn it back on without being physically at the printer. The definition of off means that there is no functional radio for you to connect to. So, what you are asking for is impossible.