Browsers may support more aliases because they do not have a sufficiently advanced encoding detector, but have discovered supporting certain aliases can help. Currently there is no standard for detecting encodings.
Since many encoding specifications do not define the mapping for each octet there is a certain freedom for browsers to do something different from other browsers when it comes to those undefined octets. These octets are also less likely to be found on the web as text editing software would not typically generate them so interoperability is not much of an issue.
Browsers support encodings the operating system has used to support for ages without there being a need for it on the web. Chrome uses the same architecture for encoding support as Safari, but it has only activated support for twenty-eight 8-bit encodings. If we can assume that Google used data analysis here as well to figure out which encodings to support — they have gone to great lengths to make foreign locales work — it means that most browsers are simply too “complex” here. It is “complex” as supporting additional 8-bit data tables is not all that complicated.