Django is optimizing for the 99.99% of people rather than the 0.01% of people who manage billions of rows on a single table. I like SQLAchemy, but for most people the added cost of managing connections, transactions, have to decide whether to use the 'ORM' or not, manually having to 'commit' changes, eager-loading vs. lazy-loading, is a complete waste of time if all they want is a website that will be used by - at best - a couple hundred people concurrently.