They're no longer that popular anymore. They are only ranked 24th in terms of trading volume per 24h now, compared to Binance which is currently number one. This is far from their peak where they were consistently getting the #1 spot.

Their reputation has sort of been ruined by their terrible support and just generally pretty bad experiences that customers had had in the past. Especially as they forced verification onto every single user, that was the start of their downfall.

Anyways, I think that the reason that some people still use them is probably because that one, they are used to their trading interface from the past, and two, they've got some pairs that are not being traded on any other major exchanges. Apart from that, I don't see any advantage in using them over Binance tbh.