If you've been to any new playgrounds lately, you may have noticed there aren't any monkey bars or rings being installed any more. Many items are no longer manufactured and sold for playground installation, due to being deemed unsafe based on on playground injury statistics.
The problem with monkey bars is based on children using playground equipment in unintended ways, which is very common when kids access their inner creative explorer and get the idea to try something different. Walking across the top of monkey bars is hardly original, should always have been expected, along with the related injuries most common on them. Children rarely, if ever, consider the potential dangers until it's too late, they're falling and about to impact something.
Rings are a slightly different story, remember how some of them used to clang together? There was often that one ring at the end that was larger than the rest, and if another ring swung toward where you were holding, it would smash your hand and fingers between these heavy metal rings, normally causing the release of hand grip and a fall.
There are a number of pieces of playground equipment that have been banned, many of which are completely understandable, especially some of those really old ones like the merry-go-round, where the most fun was trying to see how long someone could hold on while it was spun as fast as possible, before slinging anyone on it outward, often impacting other structures or kids. We really don't know what we don't know until we know it!