Apple doesn't make it easy, but they don't make it impossible either, and at this point it's on the ecosystem to show Apple they want more of this by embracing what they have. So, sure, map links tend to open Apple Maps by default, but they can offer the user the choice to use other mapping apps, which they can check for by seeing if the OS will respond to their open url scheme. Harder? Sure. Impossible? Nope.
And for what it's worth, open a directions link from Google some time - for me, it opens Google Maps, which I do have installed, but don't prefer using. I choose Apple Maps because I'd rather have Watch notifications while I drive, but Google doesn't offer me that choice.