They send a really interesting message. Now, presuming an essential part of the game isn't lock away behind a micro-transaction or the function of a micro-transaction isn't the banishing of ads, the message of micro-transactions seems to be "pay us money to not play our game".
This could be a device of the reward being greater than the experience. People might grind for an achievement or superfluous emblem in a game in a way that isn't enjoyable to play so repetitively. Isn't that strange to anyone?
Take Mass Effect 3. You can pay to get extra credits to unlock more gear. But you can get more credits by playing the game, y'know, the game you supposedly bought because you'd enjoy playing? So now you're paying X amount of dollars for a game and then paying small amounts on top of that to avoid playing the game.
I would have thought that if you wanted extra credits you'd play the game to get them because the game is a rewarding experience and you get rewards by experiencing it, y'know you enjoy the gameplay and then the game rewards you, then rinse and repeat. If the game was fun to play why would you pay money to skip playing it?
Then it makes you wonder. Do designers purposely make their game not fun to pay unless you pay little extra fees? Do they create a desirable reward for players that could be obtained by playing the game repetitively but then hide it behind an amount of repetitive gameplay that is mind numbing and boring to achieve no matter how fun the game is?