Make sure to read the article, not just the title. They're not being fined because they're dominant, they're fined for anti-competitive behavior (aka bribe).
> Qualcomm [the market leader at the time of events] illegally shut out rivals from the market for LTE baseband chipsets for over five years [...] Qualcomm paid billions of US Dollars to a key customer, Apple, so that it would not buy from rivals. These payments were not just reductions in price — they were made on the condition that Apple would exclusively use Qualcomm’s baseband chipsets in all its iPhones and iPads. [...] This is illegal under EU antitrust rules and why we have taken today’s decision.”
> Qualcomm [the market leader at the time of events] illegally shut out rivals from the market for LTE baseband chipsets for over five years [...] Qualcomm paid billions of US Dollars to a key customer, Apple, so that it would not buy from rivals. These payments were not just reductions in price — they were made on the condition that Apple would exclusively use Qualcomm’s baseband chipsets in all its iPhones and iPads. [...] This is illegal under EU antitrust rules and why we have taken today’s decision.”