Here's why:
* Romance languages evolved from Latin. French, Spanish, Italian, Portuguese, Romanian, and many others are Romance languages because they developed from the Vulgar Latin spoken by the people of the Roman Empire.
* English has a different origin. English originated from Germanic languages brought to Britain by Anglo-Saxon invaders. It was later influenced by Norman French after the Norman conquest in 1066.
While English has borrowed many words from French and other Romance languages, its core grammar and structure are fundamentally Germanic. This makes it a Germanic language, alongside German, Dutch, Swedish, and others.