Very common problem that, as the article says, is hitting everyone, even successful digital platforms like Spotify, Sirius, and more.
The particular problem that WBUR faces is it's a single radio station without a TV station. By contrast, WGBH has TV as well as some additional radio stations to combine in a platform. WBUR also hasn't created a really successful podcast. In this multimedia world, it is important to diversify, and offer sponsors multiple platforms to reach users. I say all the time that radio needs a second revenue stream. For public radio, that second stream was corporate sponsorship. Now it appears they will need to find another option.
In another thread, we were talking about a shortage of good mid-day talk programming for stations. At one time, WBUR was part of Talk of the Nation, and Here & Now was a successful nationally syndicated show. The advantage of national shows is it offers corporate sponsors a wider audience. It might be a good time for WBUR to look at its resources and see if it might be able to create another national show.