Above all, a bicycle with narrow tires is much easier to accelerate because the rotating mass of the wheels is lower and the bicycle is much more agile. At constant speeds of around 20 km/h, the ride is better with wider tires. In practice, the energy saving is even greater than in theory as the elasticity of the tires absorbs road shocks, which would otherwise be transferred to the rider and so saves energy.
I'm sorry, but the weightloss between 21 and 23 mm tire is so small that it's almost certainly undetectable in accelerating speed.
Aero beats weightloss every time, especially with wheels (hence diskwheels)
1. The pro's simply don't know better (Most cyclists still don;t care about tech)
2. The gains are so small that it's not worth the hassle of rebadging non-sponsor gear.