The reason companies use lots of live data is because people get upset when facial recognition doesn't work on people with different skin colors, voice recognition doesn't work for people with accents, etc. Doing #3 is literally the result of #4.
Keep in mind that there's no rule that says there must be a correct answer. If the only way to do something is approach A or approach B, and people don't like either approach, then other options include figuring out a new approach C or not doing the thing.
This is in no way 'the reason'. THE reason is that using live data without having to bother with consent is 'fast, easy and cheap'.
Having to get consent is seen as a nuisance, and num's the word as we don't want to wake sleeping dogs. And we don't want to pay for generating training data, so yeah, we basically just steal the data from our uninformed users without their consent. I hope the GDPR will pursue this as a landmark case.