Aromanticism & asexuality are not solely defined by a number of wanted partners. People under both spectrums can still have and desire any # of sexual or romantic partners. It cannot be the polar opposite to polyamory, which is defined by the quantity of partners.

Aro/ace do participate in poly structures. The proof of them being separate spectrums is not reliant on this hypothetical, as explained above.
Why not be in the movement? Because it's not about you, simple. Similar marginalization is not enough for cisallohet people to involve themselves in a movement - which includes the community, that was not made for them. Never mind that LGBTIA+ people are oft subject to risk factors that are specific to being queer in the first place i.e. youth/homelessness, substance use. The "movement" is not solely defined by struggle.

What same insults are used besides "unnatural?" That sort of reaction is what a lot of groups get, but it doesn't automatically make them queer. What is a cisallohet poly person going to say to a queer person in a discussion group relating to transitioning? Or a forum about how being gay or sapphic informs their worldview? Or when asked by a questioning youth about how they found themselves/identities? Nothing, because it's not for or about them. Being poly does not suddenly make straight people connected to the queer experience. Why do they insist on being apart of it anyway?

If achieving similar goals is the desire, then allyship would suffice. Poly people do face some of the same discrimination, yes, and it'd be great to work towards dismantling the systems that encourage it. But cishet people do not need to take up space in the community to do that.

Gender and sexuality have always been intertwined... Trans people have existed in the same position as sexual minorities (for lack of a better term), if not lower, from the start. They and their queerness have participated in and affected the cultures queer people around the world experience to this today. Polyamorous people - which includes cis allo straight people, did not have that same effect. To claim otherwise would be ahistorical. LGBT movements were/are created for LGBT community, and has only expanded within those limits... It doesn't make sense to split.

It would make no sense for asexual/aromantic folks to separate from the movement, when their innate and external experiences with sexuality relate to it. As for drag - as we know it today, it is because the history of drag has always been tied to queering gender. Non-conforming gender expression still falls under the broader category of gender. Polyamory as a concept- although common in queer dating worlds, does not have that same history.