After selecting a word, sentence, or paragraph and selecting Speak, why does it not keep reading?

This is by design, as Speak is most commonly used to hear the pronunciation of a single word or sentence.

To enable text-to-speech to run continously:

1. Tap the Control icon (looks like a gear wheel)
2. Scroll down and tap Speech Synthesis (text-to-speech)
3. Toggle Speak all on

Once started, speech will now continue until the end of the book or it is stopped by the user.