Why does Sri Lanka have so many economic problems?

Trying to understand where Sri Lanka stands in terms of progress and growth and what's stopping it from become a mid-high income country.

Compared bigger South Asian economies, it has far lesser corruption, better education system, at least at lower levels, is cleaner and has better tourism prospects. Yet it seems like they have failed to have stable governments, institutions and economic policies and their biggest port is owned by China.

So what's happening there and what went wrong?