When they say they will burn a portion of the tokens, some people think that with burning the tokens and decreasing the total supply, token's price will rise and buy the tokens before the burning.
In this way, they deceive many people.
Newbies don't pay attention to the fact that they are burning the tokens that have been created by themselves from the thin air.
They can easily create as many as tokens they want and then promise to burn them. This doesn't make the tokens valuable.