It is _the_ 2FA device. from SMS, to authenticators, to password managers, etc. It also has access to all of your personal information, your pictures, your contacts, your email. It actively receives notifications and messages from the outside world, from potentially any sender. It's connected through WiFi, GPS, 5G, bluetooth, UWB, every possible connection system imaginable. It can listen to your phone calls, read your text messages, interact on your behalf with pretty much everything in your life, and is a single facial recognition away from automating emptying your bank account. Not to mention the fact that mobile software does tend to want to at least survive a little bit when offline, so plenty of data is stored locally.

It's a key to your life. The perfect target for any attacker.

My Linux laptop is my 2FA device (email), it holds my passwords, and personal data like photos, contacts, email. It receives notifications and messages from outside world from potentially any sender. It connects through Wi-Fi, Bluetooth, Ethernet, 5G (built in WWAN). It even has cameras, microphones and I use it for my online banking and shopping. The only reason why smartphones "need" to be ultra secure is because everyone and their mother have one and the truth is most people can hardly tell a difference between their head and their butt.

Well yes. Security measures aren't for the principled tech saavy scene who is up to date on the latest malware and exploits. That's how Apple rose to power; it put convenience first and told users it'd worry about all the privacy stuff for them.

A bit contradictory, but that's what the people want. They (as a mass) always choose convenience over both freedom and security. So that's why we always converge towards a centralized power, in tech and the larger world.

You just described a computer. There is nothing in your list that is mobile specific.

Because regular users (non-techies) install all kinds of apps on their phones, from all kinds of sources/vendors, but not on their desktop. Most people use only a handful of applications on their desktop (browser, office suite, …) but they have dozens if not hundreds of different apps on their phone.

They aren't, unless you want to run untrusted apps outside of a distribution.

Flatpak sandboxing is a thing however, and probably good enough in the meantime.

Flatpak sandboxing is not good and development is very slow.

It's good enough for people running trustworthy apps. Certainly, no worse than your PC. Also we don't need flatpak to be developed quickly.