I'm not sure of the color inheritence in Sibs but everything else can be chalked up to generations of poor breeding practices.
In GSDs there is a sudden surgence of brindle GSDs. Yes, there were brindles in the dogs used to form the breed but brindle is a dominant color. It was very easy to breed out by simply not breeding a brindle dog. There haven't been brindles in GSDs in 100 years. Suddenly, they are all over the place. "Old Fashioned" and "It's just an original color re-emerging" and a ton of other excuses.
Personally, I'm looking at the fact that there are suddenly brindle GSDs and comparing the timing to the increase in popularity of Dutch Shepherds. Dutch Shepherds are brindle and the average Joe thinks that every long nose pointy eared dog is a German Shepherd.