The joys of indirection.
In trade for building the tooling around managing that parameterization, Google gets...eyes. Eyes that need to manipulate tags are eyes that need to buy tags, consume the information those tags have generated. But even if that market doesn't pan out, it extends Google's knowledge of who is reading what, where, which of course is the flip side of search: not just spidering content and seeing how it relates to itself via links, but observing users and seeing how they relate to content. This is valuable data, and whatever you spend on "free" tooling is probably justified.
Smart.