In what cases is using ClickHouseDb and the like a neccessity?

An open source for website analytics - https://github.com/plausible/analytics They use Postgresql and ClickHouseDb. When it comes to web analytics, there're tons of events going that need to be tracked. From the point of view of database, why is using ClickHouseDb in this project neccessity? Why wouldn't Postgresql, which is relational database, alone do? Yes, ClickHouseDb has been created specifically for analytical processing. But still, why wouldn't Postgresql **alone** do? Are Postgresql, MySql and the like uncapable of handling lots of inserts that occurr simateneously?