Why are the images for the mods different depending on the modloader?

[Jouto25]

I've noticed that the images used for each mod on an instance can depend on what modloader you use.

For example, this is an instance with the Fabric modloader:

And this is an instance with the NeoForge modloader:

Is there a reason for the different images used for the two modloaders mentioned?

[Trial97]

The image is fetched from the mod jar file and not from the provider(Curseforge/Modrinth).
On fabric/quilt that image has a few constraints (imposed by the loader) that the image needs to be square.
On forge/neoforge that is not the case leaving the mod authors more freedom in choosing the image they want.
As for why some mod authors want to have different images on each loaders, you can ask them.