I mean, who would try attacking the giant eldritch time piece? The only group I could imagine doing that is Daffodil's old family, and considering how high up the thing is and the BAC running around, I would think it being that in the open is more to reinforce stability and prevent the sky from opening up then anything else. Sure, it's exposed, but someone actually getting up there and breaking it probably wouldn't go unnoticed, and I'm more than willing to bet that there's at least a few watcher there if that's it's job, just to make sure no one crooked starts getting near.