Why are UART, SPI, and I2C all poor choices for sending data across a machine or vehicle?

They're designed as short-haul, on-board buses using single-ended (ground-referenced) signaling, which doesn't tolerate distance or electrical noise. Over long wires, capacitance slows the edges (especially I2C, whose open-drain pull-ups already limit rise time), ground potential can differ between distant boards (single-ended signals reference a shared ground that may not be truly shared), and there's little to no noise immunity or robust error recovery, a glitch corrupts data with at best a parity/framing flag (UART) or nothing (SPI). For distance and noisy environments you use differential buses: CAN and RS-485 send each bit as the voltage difference between two wires, which rejects common-mode noise and tolerates ground shifts, support multi-drop topologies, and (for CAN) add arbitration and strong error detection/recovery designed for vehicles and industrial settings. So crossing a chassis or a factory floor moves you from the chip-to-chip trio to a differential field bus; USB is the answer when you instead need high-bandwidth to a host.