This fine would only make sense if Microsoft prevented users from installing a different browser. Consider an analogy: let's say there's a power company who runs a monopoly on generating electricity. They also provide natural gas services to their customers. There is, however, a bunch of other smaller natural gas companies just a phone call away that people can buy natural gas from; all you have to do is call them an…
And for that sin, MS will keep paying for a long time; they're basically an ATM for the EU now. This is not great but hey, they do have a history; once a felon, forever a felon, so to speak.