I’m not 100% sure but I guess it’s because usage of @uses can be covered with @see
From phpDocumentor docs
@uses is very similar to @see, see the documentation for @see for details on format and structure. The @uses tag differs from @see in two ways. @see is a one-way link, meaning the documentation containing a @see tag contains a link to other documentation. The @uses tag automatically creates a virtual @usedby tag in the other documentation that links to the documentation containing the @uses tag. In other words, it is exactly like @see, except a return link is added automatically.
The other difference is that @uses only accepts one element to link to, and a description of that element.
Probably, WP people decided that it isn’t worth to have 2 tags so similar but only maintain one.
BTW, @uses is a fine tag. If you want to support it just do it and document its support in documentation.