Like many free software projects, GIMP is facing some challenges that cannot be easily worked around.
Both decreasing activity, lack of centralized crowdfunding efforts, and little work on usability are mostly the result of lacking human resources.
Simply put, the only way to make it right is to get busy.
I doubt many people at Adobe worry about competition from GIMP eroding proprietary profits, an essential metric.
GIMP does not benefit from a strong central organization and a driven entrepreneur, like say Blender does.
Will GIMP development pick up speed as some longstanding development milestones are reached and interested people get busy? Or will some central actor step up to coordinate large fundraising and promotion efforts? Or will something like snowdrift.coop prove central to relatively bottom-up coordination? Or will GIMP never seriously threaten the profits of proprietary incumbents? Or multiple, none, or other?
20 years of such an important free software program is worth celebrating in any case. GIMP users-developers (and producers of the libre film Ze Marmot) Aryeom & Jehan made some nice cartoons. Another is at the birthday post.