This is not only because of people buying them and placing buy orders. Pump&Dump groups pump lot of shitcoins daily, and after that people buy more because after the dump, coin is 20-50% more than before so people just buy them because they are cheap and are getting higher.
I used to buy in Cryptopia between $25-$50 of some shitcoins recently listed. After that I always place a sell order for 3-5-10 depending how many satoshies they costed me. I was lucky that some pnd groups picked some of this shitcoins and I got BTC when they hit my 3,5 or 10x sell order

This is happening more and more. Lot of people also buy shitcoins because they know that maybe a pnd group could pick the coin.