Mjolnir does a lot of the work
Thor doesn’t need to be front and centre for the reference to be clear. The hammer alone is often more than enough, and works on everything from small items to clothing and graphics.
T-shirts give Thor and the thunder motif plenty of room. Posters make space for film versions and bigger scenes, while smaller products can let Mjolnir be the whole point.
The hammer also makes it possible to create Thor merch without using the character himself every time. It gives the design a cleaner Marvel look when the symbol is enough.
Asgard without all of the Avengers
Thor on his own keeps the focus on the character, the hammer and the part of the Marvel universe that belongs to Asgard. It has a different feel from a broad Avengers page with all the heroes together.
Find more from the same universe under Marvel and superheroes.