What was the rationale for reverse brake levers?
If you look at drawings of old bikes, both types of brake configurations are depicted. This supports the idea that it was merely a design choice with no significant pros and cons over other configurations other than aesthetics. I suggest that it just so happens that builders in the place and time period you cited used this design because it was fashionable.

There is very limited risk here for "catching" unless the rider is literally going through shrubs (and in that situation, catching would be the least concern). Also, bizarre freak-accidents aside, no one is going to be "speared" by a reverse brake handle. Think about what would actually have to occur for that to happen.