You do this every time you use your microwave? Because we're talking about making around 6 - 10 cups of tea every day for everyone who happens to be in the room. It'd be a little odd to go and clean your microwave before every round of tea, not to mention microwaves don't heat things evenly so you can't do them all at once, it very quickly becomes way more effort than just flipping the switch on a kettle that is only ever used for that purpose.
Tea is an odour sponge. Russian caravan in it's original form obtained a distinctly woody smokey flavour just from being too close to a campfire. It's simulated today by mixing kemun, lapsang soushong, and oolong. But tea will take on the flavour of anything it's left with.
Oh, I use an electric kettle for tea and coffee for that matter. I was just giving the method I use to clean my microwave. I clean it whenever it gets dirty enough to bother me. I don't use it often and I mostly cover my food if I do heat it up. So about every 2-3 months?
again, an unrelated point. how frequently do u use your microwave ? i would have to guess at most once or twice a day ? unless you only eat microwave meals, or think that the microwave is the only way to cook things....