Data from Alexa isn't great, because it's a sampling method, and there's a lot of bias in the way it samples, in my opinion. I don't know what similarweb uses for its data, so can't comment on that.

Size of communities isn't necessarily the main driver for overall traffic. It's likely a reasonable amount of this traffic comes from organic search, and most posts on Hive are written in English, so it's not surprising that countries where English is a primary language tend to rank well.