Why would anyone want to remember people who, quite willingly by and large, fought for a white supremacist regime? It is quite clear that the main impulse structuring the UKs involvement and its choice of allies in the WWs was the desire to maintain its empire. It is also quite clear that neither war would have happened at all or at least in the form it did without this.
Why/how could any serious student of history ignore this? I guess conformity with public opinion (produced by apologists of colonialism) is convenient.
Conscription was compulsory for all of WWII and a chunk of WWI. While defence of the British Empire was a crucial motivation for involvement in both, the idea that German (the same race as 'us', remember) victory in either would've led to self-government for the people of, say, Africa is fanciful.
Quite apart from all this, wearing poppies is a way of commemorating compatriots who've died and the impact this has on family and community. It's an acknowledgement that we're bound by ties rather stronger and more meaningful than the crass student politics with which you'd like to draw a line between the 'moral' and the 'immoral'.