A deadline changes everything
Reading about robotics and building a robot that has to work on a specific day, in front of judges, against other teams, are very different experiences. A competition forces a team to move from theory to a working system: the robot has to actually drive, actually grip, actually finish the course, on schedule, with no extensions. That pressure surfaces problems that a leisurely side project would let you postpone indefinitely, like a wiring harness that works on the bench but shakes loose during motion, or a control loop that behaves fine in a demo but falls apart under a judge's unpredictable test run.
This is why competitions are such an effective teaching tool. They compress the full engineering cycle, design, build, test, fail, and fix, into weeks instead of years, and they make the cost of skipping a step immediate and visible. A team that skips testing doesn't just get a lower grade, it watches its robot stall in front of an audience.