Many art-worlders have an if-you-say-so approach to art: Everyone is so scared of missing out on the next hot artist that it's never clear whether people are liking work because they like it or because other people do. Everyone is keeping up with the Joneses and there are more Joneses than ever.
Cubism was an attack on the perspective that had been known and used for 500 years. It was the first big big change. It confused people: they said 'Things don't look like that!'