You can come up with a new coin with the supply of 50 billion coins and when you trade one for a dollar, market cap will look like it is 50billion$. This is exactly what is going on with ripple especially. I don't know about the others but i am pretty sure many of them are scam like ripple as well.
Without real demand from real people, market cap. is a worthless parameter.
I'm not sure, but you may be right in a way on the Market Cap. But what about Trading Volume(24)? Ripple has over $290 million in trading volume today, for example. This is something different from what you've mentioned, right? This means lots of people buy it, and I don't think most of them are from the Ripple team.
There is a thing called fake trades, where one buy his own coin and sell it to himself to produce volume and make the currency noticeable, making people think that there is a big demand for that coin. The question is why does this coin keep on producing several thousands of BTC volume and yet never depleted the supply. One example is XRP.
This works only with coins with trading volume under $100k. When you have over $200 million trading volume in 24h you will lose so much on fees doing what you described that no one wants that.