Different parts have different life times
When a PC gets tangled in malware, most of the public go to PC World and buy a new monitor, keyboard, mouse, box, power supply, DVD player, hard disk, motherboard, super-duper CPU, RAM and graphics card. Anyone with basic computer literacy and a screwdriver updates only the parts that will make a difference when required.
I have wanted standard laptop components for decades, and they are now approximately practical (tape a monitor into the lid of an attaché case and a raspberry Pi with some USB components). Much of the cost of a laptop is the display - the second biggest cost is the bundled crap that is inflicted on me because of segmentation. Modular laptops would save customers lots of money, which is why the OEMs do not make them.
Modular phones do not exist for the same reasons as modular laptops. (Does Dell still swap some pins on the power connector to annoy customers who want to upgrade their PSU or mother board?). If love the idea of a modular phone. The only way they will exist is as a bunch of DIY components. Some people would like to pay for a quality camera. Others would like to save money there. I would like a physical off-switch for the microphone. I would like a good display, but not have to replace it when I upgrade to a more efficient CPU. I do not want to replace the entire phone when the battery no longer charges.