I do get the pleasures of sweet milky drinks in general, and sweet milky matcha drinks in particular. Matcha plays well with dairy and sugar; there's something that just hits the pleasure centers, so it's easy to understand why sweetened milky matcha drinks are so popular.
Another reason sweet milky matcha drinks are so popular is throwing fat and sugar at matcha is a good way to make bad matcha powder palatable. Low-quality matcha, prepared with water only is a very, very hard sell -- as my eight-year-old daughter Daphne has succinctly explained: "bad matcha reminds me of a kid's neglected fish tank -- if you scraped the green stuff off the sides of the aquarium and made tea with it, that's what bad matcha tastes like."
And indeed, that's pretty much exactly what it tastes like! So it's no wonder that adding milk and sugar to it is really the only way to use it.
Good matcha changes everything, of course.
Please don't put milk in your good matcha, especially if you're drinking it for health reasons. The milk sticks to the polyphenols, which alters (not in a good way) the bioavailability (how well your body can absorb nutrients) of the matcha, and all the goodies just flush through.
There's a large body of research that concludes that polyphenols play an significant role in preventing and in reducing the progression many diseases, including diabetes, cancer, cardiovascular, and neurodegenerative diseases.
Polyphenols too play an important role by increasing the ratio of beneficial bacteria in your gut, which is important for health, weight management, and disease prevention.
You want polyphenols in your diet, and good matcha is chock-full of them. But if you put milk in your matcha you're taking away much of the goodness, so please stop doing that! They key is to drink better matcha. You won't even miss the milk.