It's curious. In several shamimomo fanarts, artists portray Momo in an assertive, direct or even seductive way. But, both in the anime and in the manga, it has been shown several times that Momo is shy and dishonest (at the same level as Shamiko) when it comes to showing her true feelings ... Of course, I dont have ploblems with it : )
^ I noticed that too, and I think it's because that's the first impression they got of Momo before she started showing her true self, in the first episodes she was stalking Shamiko to the point she even entered through the window once, and Shamiko was scared of her, of course they developed a lot since then but first impressions matter a lot and she looked to be the deadpan pervert/romantic assertive type of magical girl similar to Homu.
@Maximus66
Not really. Later, in the manga, there were some moments when Shamiko became affectionate to her. Momo's response: physically assaulting her stundere style.
As in this fanart (it is practically the same as a particular scene of volume 3, but without the costume exchange): https://danbooru.donmai.us/data/sample/__chiyoda_momo_and_yoshida_yuuko_machikado_mazoku_drawn_by_hiroshix31__sample-f1d8754bb87b6e5b12d0c55c3579de03.jpg
In fact ... on second thought, Shamiko is the assertive of the relationship. She is more open showing her affection, she was the one who invited Momo in all the "dates" they had (there was more in the manga after the final chapter of the anime), she is not afraid to tell momo about her insecurers or ask for advice, and technically she was the one who confessed first, if you take the scene in the sakura tree as a confession.