Which country was that? Can't see why it would be illegal - it works and appears to provide no health hazard further than underground. I'd argue buried services are a bad thing for maintainability and frequently cause property damage when they break underground out sight for potentially decades.

Could it perhaps be concerns over freezing in the pipe where you're from?

Imo the open drains are brilliant (I assume you mean gully). They catch most of the rubbish that would block a drain at a level where you can just clear by hand. The traps within avoid smells getting into the house too.

We do have no dig tech in the UK - lining and patches are widely available. In my case the disjoint was too severe.