Yes, this. ^ Why would it be a 'class' thing? Why even say that?
As many posters have said, I wear it (and hang a 'we shall remember them' flag in my front window) out of respect for the fallen, and the dead, and that includes 2 great uncles of mine, and some of their friends. My grandfather fought in the second world war, and was shot and badly injured but survived thank God .. He lost some friends too. They all lost people: friends, cousins, siblings, uncles... My great grandather fought in the first world war and died, and so did his brother.
I have known numerous people - men and women - who fought in The Falklands War, and Desert Storm. (1980s and 1990s.) Some died, some came home. Wearing the poppy is a sign of respect to the injured, the fallen, the war dead, (and the military in general for their service.) And yes, because they died for our freedom! I have a purple one too, for the animals who went to war too.
I am gobsmacked that you are even asking this @oiolehnvn and couldn't have just googled it. I'm also surprised at you using the word 'naice.' 
It's also ridiculous to say it's performative to wear a poppy, as @HostaCentral said, and is an insult to our military, and the war dead. Disgusting comment. 
As for the comment that all right wing people wear them? ( @Giddykiddy ) Do me a favour. You see 1000s of people wearing them. How the hell do you know they're all right wing? What a ludicrous comment! Also, so what if they're right wing? What's wrong with being right wing?