Adam has an aspiration for cross-platform comments that serve as their own meta-content to a show that goes with the show regardless of which app the listener uses. He also opposes a payment requirement to create comments. Separately from this, in Podcasting 2.0 and Moe Factz w/ Adam Curry, boostagrams serve as a parallel payments methodology to fiat money, as a means of the audience sending in comments and letters to actually be read by the host, sometimes on the show. On No Agenda they read the names of anyone donating over $50, and read the letter of anyone donating over...maybe it's $200, I can't remember. They'll read dozens of names and sometimes a dozen letters. Right now with the boostagrams, on the aforementions shows, they read the boostagrams at rather paltry amounts.

tl:dr Adam didn't want boostagrams made public