Because leveraging bundling is illegal, if the bundled item is a monopoly, in both the US [1] and the EU. Further, leveraging their search monopoly in such a way as to juice other products is to the detriment of users: if the product deserves a given space in the search results (where deserves means would rise there without bundling), it should rise there on its own, or there is a better alternative that should have been there instead. Hence user harm.

[1] http://en.wikipedia.org/wiki/United_States_antitrust_law