There are few plausible thoughts…
1. If Barto did activate his barrier and Sabo just casually went pass him... Barto should reacted differently like "How...? or Who the hell is he... cancelling my barrier like that!" because he didn't know that guy & "that guy" might harm Luffy.
2. Maybe Barto wasn't paying attention because he's focusing all his anger on "that guy"
3. Sabo didn't activate his Haki and so does Barto didn't activate his barrier as well...
--- Update From New Post Merge ---
@kuma:
I hope DD crew are strong if baby 5, Buffalo and Jora are anything to go by I have no confidence they can handle what's coming there way.
Baby 5 & Buffalo couldn't handle General Franky already… :happy: