Yes, their marketshare overall is lower however in certain very large EU countries their market share is very high and their practices shouldn't escape scrutiny as this type of law also applies to smaller players. I suppose it's an issue of allocation of resources for the regulators. Smaller has less impact. The individual country regulators can also address this.
When there's only two competitors and the margin is only 20% in some subset of the population, that's not "very high market share." EU-wide, Android is >70%.