Focusing on the absence of stimulation:
* On aime l'art parce qu'il est reposant. (We like art because it's relaxing.)
* On apprécie l'art pour son calme. (We appreciate art for its calmness.)
* On trouve l'art apaisant. (We find art soothing.)
Focusing on the slowness and contemplation:
* On aime l'art pour sa lenteur. (We like art for its slowness.)
* On trouve l'art fascinant dans sa simplicité. (We find art fascinating in its simplicity.)
* On est captivés par l'art dans son immobilité. (We're captivated by art in its immobility.)
Playing with the paradoxical nature of the statement:
* On aime l'art pour son ennui. (We like art for its boredom.) This is a very direct translation, but it might be perceived as a bit ironic or provocative.
* On aime l'art parce qu'il nous permet de ne rien faire. (We like art because it allows us to do nothing.) This emphasizes the passive and contemplative nature of appreciating art.
Ultimately, the best way to express this idea in French will depend on the context and the specific meaning you want to convey.