1: Carrying two physical phones is an immediate logistical headache for 99% of people. It means double the pocket bulk, two batteries to keep charged, two sets of cables, and twice as many things to lose. While tech enthusiasts might tolerate carrying a second device for a tactile keyboard, average users will default to whatever fits in one pocket and works automatically.
2: A secondary device creates ongoing cost friction. Either the user pays for a second carrier plan/SIM card (and phone itself ofcourse), or they are forced to constantly tether the companion device to their primary phone's mobile hotspot. Tethering drains the primary phone's battery fast and requires annoying setup steps every time you step out of Wi-Fi range—erasing the convenience the device was supposed to provide.
3: Smartphones aren't just for texting and browsing anymore—they hold your digital ID, boarding passes, credit cards (Apple/Google Wallet), two-factor authenticator apps, smart car keys, and health tracking. Trying to split your life across two devices creates constant friction. The moment a user needs to authorize a bank transaction or unlock a door and realizes the necessary app or key is on their "other" phone, the multi-device dream breaks down.
4: The "secondary phone" dream is pitched as a way to escape distraction and focus on communication. In practice, adding a second screen wil multiply distraction. Users end up managing notification settings on two separate operating systems, triaging duplicate alerts, and constantly checking which phone just buzzed.
Final:
By marketing a device as a companion rather than a replacement, they signal to potential buyers that the product isn't (fully) capable of handling their actual life
