WhatsApp has made encryption easy, easy to use and easy to understand. Just the day before my mother received a notification saying her WhatsApp messages were now encrypted. And she understood right away.

Sending a GnuPG encrypted email on the other hand is way too much to ask for the layperson.

Getting the message sent and successfully received is of more importance. It's better if its also encrypted. It's best if the messaging and encryption work together, seamlessly.