Because they don't know about bitcoin and they don't believe and what is bitcoin. They keep saying on this because the price is getting low and higher so they stop talking about it. Those people had no bitcoin so they keep saying that. Don't mind them one thing is to do them we prove that they are wrong. I don't know why they saying about it impossible to happen bitcoin is dead or else do not care on bitcoin.
They say it because they want to divert the minds of people from bitcoins and they have a feeling that listening to negative news related to bitcoins they will get panic and will start selling their coins but now that will never happen as people are well aware about the potential of bitcoins.
And they just envy us, successful investors. We buy bitcoin and our money grows. And they believe in their fiat, which only depreciates every year