"Signal is being blocked in Venezuela and Russia. The app is a popular choice for encrypted messaging and people trying to avoid government censorship, and the blocks appear to be part of a crackdown on internal dissent in both countries..."
You need a certain market saturation before a ban becomes useful. If very few people are using the service, there's little incentive to invest time/energy in a block.
I suspect the recent wave of riots in the wake of the election is driving the urgency.