My guess would be that it would take quite some time to respond to everyone hitting the emergency button. That's just a guess.
As for no mass announcement, that sounds like an easy win for corp to mandate, UNLESS they have already heard otherwise. My ASSUMPTION is that if enough ppl complain about, or suggest a mass communication after x minutes of stoppage, then a mass announcement will happen. Seems pretty simple. They may have planned the announcement, but the need for the announcement was "cleared," because the op says there was stopping and starting several times.
OTOH, they may have already researched this extensively, and they know that a mass announcement before x minutes will cause people to freak out even more.
It SEEMS, on the surface, that after every few minutes, a mass announcement of: "Experiencing a delay, please stand by..." and then maybe a few stupid Disney facts or jokes would suffice for me, BUT, it might also make some ppl lose their marbles, I don't know. I'm not freaked out by heights, too much. I mean, I am to a point, but I also LIKE that scared feeling - it's a rush.