Because of the effort involved. At least for me, learning how to read in a foreign language is far far easier than learning how to understand the spoken languag

Because of the effort involved. At least for me, learning how to read in a foreign language is far far easier than learning how to understand the spoken language and learning how to produce the spoken and written forms of the language. So, I can either learn how to read, hear, speak, and write a a single language or I can expend the same effort and learn to read many languages. For me, the later is much more appealing. But then, I'm a voracious reader and too introverted to be interested in talking or writing to actual living people.