Defaults matter because many people won't change them, and even people that will change them aren't going to change them every time they touch a new system. Especially when the "defaults" have been that way for decades which brings a sense of gravitational pull back to those tools/sites even if the new defaults change.

Some defaults can absolutely be over ridden by a non-stop barrage of interstitial pages and ad banners imploring your to install Chrome because all the default tools you use are Google sites, which just circles back to defaults mattering.