"Be healthy" is a misleading and unhelpful slogan and goal.
Most young or middle-aged people in their 20s, 30s, and 40s enjoy "good enough" health. So being healthy isn't a very inspiring or urgent call to action. It's a low bar that they have already hit.
The health issues start in their 50s and beyond.
Fitness, as measured by strength, speed, flexibility, or endurance, is a much better goal because most people would agree they aren't fit enough and fitness is actually a leading indicator of long-term health.