Unless they live in or very close to Mecca, aren’t they just praying towards space?

My answer to your question is hidden in this question:

"How can airplanes fly from one city to the other when the Earth is round?"

It is simply a matter of directions, irrespective of the fact that earth is not straight and also that the earth is continuously in motion.

Moreover, facing towards Mecca (or precisely towards Ka’ba) DOES NOT mean that Muslims worship (or bow to) Ka’ba or Mecca… it is merely a symbol of unity!