Imagine an old house, with timber frame windows, no locks just casement stays. Night latch, single cylinder door locks. Single bolted basement hatch.

Most PCs are that house, which someone has tried to make secure by adding more locks to the places they know are weakly secured.

Phones are a modern house with triple glazed PVC multi-point locking windows and steel frame multi rod security doors.

When you take something big and complicated that was never designed to deal with modern threats and you try to secure it, you can make it pretty good, but there is always the risk of gaps. When you design something to be secure from the start it's easier to ensure no gaps... But of course neither is perfectly secure.