I'm the one grasping at straws?

Yes... that is what I said.

You think it's hard to avoid painting a picture of humans from behind that isn't sexual! That is completely absurd!

Any realistic/reasonable suggestions...?

the most notable thing about this painting are the asses,

Right, because humans, themselves, are sexual. Of course a lot of people, especially male, will focus on the asses. That doesn't make the image "blatantly sexual".

and it literally has nothing to do with the theme.

Of course it does. First, the most prominent is probably the astronaut, who is female. That's probably at least a little significant. In any case, these astronauts are the "new".

Second, the girls in the short frock-like things are obviously in some kind of traditional clothing related to celebration, ritual or some other purpose. These are the "old". If you look back at older cultures in our world (I would "like" to think that this image does not depict a scene from our world) many of them were far less modest and wore less clothing. This seems to be a reference to that kind of culture. Honestly, I think it would have been better if there had been a completely nude girl (or boy? girls seems better though) amongst the crowd as it would stand out even more as something that doesn't seem to fit in with our notion of culture.

The artist was either clearly horny while making this decidedly not sexually themed painting, and/or the artist wanted to appeal to the sexual desires of the audience. That's it. Period. I'm an artist myself, and when I see this kind of shit it pisses me off because it shows just how critical the audience really is (read: not critical).

It's so hard to not fall into the trap of just assuming you are trolling.

and/or the artist wanted to appeal to the sexual desires of the audience.

Or subvert them...? Maybe they just wanted to piss people with sexual hangups like you off.

I'm an artist myself,

Yeah, okay. Do you have an example? Are you not aware of the countless other paintings - classical paintings - that depict nude people, even young women, in non-sexual ways that are only "blatantly sexual" because we humans tend to be "blatantly sexual". Come on.

It's okay if you don't like the painting. It's okay if you don't like images that involve bare skin, especially skin on parts that are generally considered risque. But don't accuse the painting/painter of being horny when doing it A) as if that would be a bad thing and B) as if that is the only reason anybody would ever put an ass in a painting.

If you don't mind me asking, what is your sex? And do you have an example of your painting (I assume you are a painter/illustrator if you think being an artist makes you an authority on painting)? Do you have an example of a painting that includes a female (or male, I suppose), that might be comparable to this but is done in a less than "blatantly sexual" way?