This is a game about genetics and breeding. The thing behind the normal deviants is called "epistasis".
I think this picture pretty explains it.
All you need is not to breed normal pattern pets. And it's not true that normal pattern pets take the same efforts. They just pop here and there when you breed for genes, so they don't take any efforts at all unless you intentionally try to get a normal deviant and breeding two homozygous normal pets again and again, but then you know what you're doing. Though I understand the rant about normal deviants as exhibition prizes (got one of them too), but it's just luck, and I tend to think that pets aren't main prizes but just a little addition to the scrolls and trophy. I'm also pretty sure that normal deviants were made like this intentionally to boost breeding for rare patterns and make deviants with visual distinctions harder to get.