Some combination of: * Javascript devs tend not to be good Typescript devs, and don't always know how to build tasteful or easy-to-type interfaces. * ...or ma

Some combination of: * Javascript devs tend not to be good Typescript devs, and don't always know how to build tasteful or easy-to-type interfaces. * ...or maybe they're perfectly fine Typescript devs, and they've made the deliberate choice to have a nasty type in order to have a particular interface. For better or for worse Typescript offers that flexibility. * Types were added after the fact and it was deemed better to have some kind of gross type for the existing difficult-to-type interface than rebuild the interface and/or implementation.