My analysis:.
I think the world wars are now leaving living memory. I don't have any living relatives who were alive during them. People aged 10, and thus in a position to remember, in 1945 would now be 88+ years old. There just aren't many knocking about and for those who actually served... Even fewer.
It's natural that the emotions associated with a particular rememberance will fade as this happens. I get a little bit irritated when people in their 60s, 70s and 80s go on about WW2 like they're proud of it when they weren't even part of it (obviously, their parents were and there are generational impacts but it does also seem to be a certain kind of person with certain political and cultural views that I don't necessarily feel on the same page as).
There is a broader cultural context also of anti-war sentiment in relation to Iraq and Afghanistan. This resulted in a bit of confusing / diluted messaging for the poppy campaign. The World War related messaging has always been about noble and necessary sacrifice to protect our freedoms in the face of a great evil. It's a good message, and pretty inarguable but it is fundamentally political and pro-war in the specific context of WW2 at least (most people are pro-war in the context of WW2 and I'd count myself among them!). However, people don't feel this way about Iraq and Afghanistan or other recent conflicts. So we are left with a pro-war message about WW2 but of course, we are running out of veterans to support from WW1/2. We do have deserving veterans from more recent conflicts but the political / pro-war messaging doesn't sit so well and people don't want to be seen to be making a political statement in support of recent wars.
In response to waning interest and memory, and to remain relevant, I kind of feel like the poppy campaign and the broader cultural connotations of rememberance have taken a direction which many feel is a bit... Distateful or insincere? Eg commercialisation of all manner of ultra expensive fancy poppy themed accessories / tat? It does feel a bit of the solemnity is lost and it's all a poppy competition. Of course the poppy campaign is not unique in tapping into commercialisation and trends of showing off in social media etc, and I can see why this trend has been basically inevitable. But it doesn't have the same earnest feel of the poppy campaign when I was a child in the 90s. The whiff of insincerity has made people a bit more cynical about it. At the same time, it seems to have become compulsory for anyone in front of a camera to wear a poppy and media hounding of people not wearing one... Sort of feels a bit like it's tapped into a culture war of sorts?
That culture war is between those who fall further toward conservatism (which always looks backward) and are viewed as adopting a rose-tinted glorification of the last century with more than a pinch of patriotism/ nationalism thrown in, and those who broadly feel much more cynical about war and the West as the "good guys". That's obviously massively complicated by and linked to generational differences / wealth distribution / political polarisation and also views on Brexit etc.
But as the one side becomes more strongly advocating of the poppy campaign, the other side becomes more... Cynical of the poppy campaign. Resentful even. Rightly or wrongly. Whilst in theory the poppy campaign is apolitical and simply about supporting veterans charities, it can't be removed from a political and cultural context. And we can see that it is different than other charities in that broadcasters/footballers etc wouldn't be shamed or hounded for not publicly supporting other deserving charities.
People who want everyone to wear a poppy often don't understand why anyone would bring up Gaza. They view the poppy as unrelated to modern politics. Even though, broadly speaking those who unreservedly support and promote rememberance these days tend to have a similar political profile.
People who feel less engaged with or more cynical of the poppy campaign often do see it as political and specifically associate it with conservatism, pro-war, pro-Brexit, pro West etc and naturally will bring events like Gaza into their perspective.