> I know a lot of people use postpaid, but I can't understand why.

Two reasons: data caps and device cost.

People want iPhones but they cost $1000 outright which isn't a small amount of cash these days so they roll the cost of the device into their monthly bill. The average consumer also doesn't understand how mobile data versus 802.11 works - their kid doesn't activate Wi-Fi on their phone or download anything, they see a large number with "GB" on the end, and they pay whatever is necessary to keep the Instagram scrolling and Disney+ flowing.

Buying an iPhone outright, flipping the old one every few years (they hold their value well) and using a $30 a month 10GB plan is doable if you have money and are savvy enough to download podcasts and use your home's AP for data.

Carriers certainly aren't incentivized to educate consumers better since they'd rather make money on device installments and milk them for hundreds of dollars a month because they "have a large family and need a lot of data". Home broadband marketing is even worse - why a family of four "needs" 500 Mbps down is absolutely beyond me. In an ideal society this type of consumer literacy would be taught in school but I'm not holding my breath.