Apple is not even close to a monopoly, especially in Europe, where they have less than a third of the mobile market. That said, the rest of the market is divided up between several different Android phone companies, so Apple is in fact the largest single mobile vendor in the EU (Samsung is neck and neck with them though, and may have overtaken them since I last checked).

So from a regulatory standpoint, Apple is the problem child even if it isn't a monopoly. The EU sees a third of its phone-using population as being "captured" by a uncompetitive foreign corporation that is far more restrictive and locked down than any of its competitors. Apple has also tenaciously resisted any attempts to open its platform by citing user security as a reason for its draconian level of control over the iPhone platform, so it became necessary for the EU to resort to powerful big-guns legislation to act. Well the big guns are here, and I don't think Apple's "user security" defense is going to be aegis enough against them.