So is population dropping? Or just ridership? Or did Greyhound suddenly have higher costs? None of that is answered in the article, unless I missed it.

<speculation:>

I assume operating such a bus line is not all that expensive, and costs shouldn't have been rising because fuel is still cheap.

So ridership must have been dropping.

So apparently they didn't need it all that much, otherwise enough people would have continued riding so that it would have stayed profitable.

That's the morale I guess: if you value something use it more often.