Because English allows it (reference : https://www.quora.com/When-is-the-definite-article-the-omitted-in-English) while Romanian requests it for the subject of the clause.
When you make a general statement about something, you omit the define article in English. For example:
- Cats have claws.
All cats have claws, so this is a general statement about every cat in the world. No need for a define article here.
Technically, to us, lightning comes before thunder simply because light travels faster than sound!