As the writer observes, the local sports anchor has been supplanted by ESPN or whatever info people get from their iPhones.
That's exactly it.
People really don't need the local news for most sports highlights. For the major leagues, places like
SportsCenter and the official league channels provide more than the local newscasts can accommodate... and for minor leagues and schools, the local newscasts are too broad to provide any meaningful coverage. Whereas a weather segment can have your meteorologist discussing in more depth the impacts of an upcoming weather events, the sports anchor in the local newscast adds nothing meaningful that the reporters haven't already added.
You can still get a decent amount of local coverage through radio, which has a smaller and more localized per-station footprint and is built better for long-form discussion. That, and weather impacts people's day to day lives, while sports is entertainment.
You also factor in the business. Mega-groups like Nexstar, Sinclair, Gray and Byron Allen (the last of whom is building an empire using affirmative action laws) are gobbling up all the mid-sized and smaller market TV stations and homogenizing them.