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The npm search command has been broken in npm for some time, as it downloads the entire package index and searches it locally. Due to the size of the index on npmjs.org, this stopped working for a lot of people due to npm OutOfMemory errors and various other issues.
Because of this, they deprecated this form of searching in the npm client in favor of a new search API, but it seems that only npm 4+ actually uses the new API.
Indexing all of npmjs.org also caused a lot of problems for our users due to the sheer amount of data involved, so we dropped indexing of any registry that supports the search API. Local packages are still returned in the /-/all endpoint, since this doesn't require the same server overhead, which is why you are still seeing those packages.
Basically, you may want to try the new npm client, or just stick to searching on the web for now.