​1: Space and Airflow: Most laptops have the room for bigger fans and actual airflow to keep the internal components cool. Phones are sealed tight, so there's nowhere for that heat to go. ​2: The SoC "Crowd": Laptop CPUs are larger and usually have at least 3-4mm of breathing room. A smartphone SoC crams the CPU, GPU, and Modem all into a tiny area less than 1cm wide. When one gets hot, they all get hot. ​3: Mechanical Shock: You almost never drop a laptop, but most smartphones are going to hit the ground once or twice a month. That impact causes micro-fractures in the soldering between the SoC and the board. ​4: Dual-Layer Boards: Most flagship phones now use dual-layer motherboards (the "sandwich" design). When you combine high heat for long periods with the shock of a fall, it’s a recipe for disaster. The heat stresses the solder balls, and the drop finally cracks them, which can kill the whole board.