Texting is expensive and mobile data for Whatsapp messages is much cheaper, even though mobile data prices are still outrageous.
In South Africa 1 SMS costs 50 cents on standard rates, and 25 cents on bundle rates. For one message. There are 100 cents in one Rand obviously. 1GB of data is around 80 Rand. If one WhatsApp text message is 30kb, 1GB of mobile data gets you over 30 000 WhatsApp texts. Meanwhile that same 80 Rand only gets you around 300 SMS’s on bundle rates.
Because you remember it better when you actually write it out instead of just using a keyboard. And you can draw diagrams with ease. Most styluses are inaccurate and one dimensional, and buying a phone with actual proper stylus support in both the display and stylus itself is expensive. You could buy a separate technical device just for note taking with proper stylus support and have it upload notes to the cloud so you can access it at all times, but that requires a constant internet connection and mobile data is expensive. And then you have to carry this seperate device with you in the same way you’d carry a much cheaper physical notepad anyways.