As the number of users of Click grows, more and more major feature requests are made. To users it may seem reasonable to include those features with Click; however, many of them are experimental or aren’t practical to support generically. Maintainers have to choose what is reasonable to maintain in Click core.
The click-contrib GitHub organization exists as a place to collect third-party packages that extend Click’s features. It is also meant to ease the effort of searching for such extensions.
Please note that the quality and stability of those packages may be different than Click itself. While published under a common organization, they are still separate from Click and the Pallets maintainers.