Zoom is still in "growth phase" which means they aren't under a lot of pressure to turn a profit at this particular moment. So they proactively offered their free service to schools, the free tier isn't time-limited, plus their corporate product is basically the same as the consumer/free product.

And on the other side, Google was totally caught napping and assumed that everyone knew about Meet. https://www.nytimes.com/2020/04/24/technology/zoom-rivals-vi... "[Google’s chief business officer] Mr. Schindler tried placating the engineer’s concerns, the people said. Then his young son stumbled into view of the camera and asked if his father was talking to his co-workers on Zoom."