Why's that? Well, put simply, because warmups work. And in the way it has been used, stretching doesn't.
Note the caveat about stretching, though. A review of the literature suggests that contrary to the notion of stretching prior to exercise to avoid injury and afterwards to avoid soreness, what we should be doing is treating stretching like strength or speed... and including it in our total routine. Not just book-ending our workouts.
But warmups, now that's another story. A warmup that is appropriate to the exercise you are about to perform really does reduce injury and delayed onset muscle soreness.
That's the conclusion reached by Journal of Science and Medicine in Sport after a systematic review of warmup practices.
The intensity of pre-exercise warmup needs to be mild and run from two to 10 minutes, with aerobic activities such as running or swimming tending to the upper end of that band. Strength exercises are best warmed up for by one or two sets of repetitions at 60% effort for the specific muscle group you're targeting.
That's the good news. The extra good news is that cooldowns - the tapering of effort at the end of exercise - apparently carry no benefits, and the research suggests you may as well forget them.
Stretching, on the other hand, should not be jettisoned. It should be included three to five times a week, and held just short of pain for 30-45 seconds, twice for each muscle group or limb.
Where did this come from? Annoyance at yet again succumbing to calf injury after religiously following the gospel of pre-exercise and post-exercise stretching.
With that simple switch - incorporating stretching into the weekly fitness training and assiduously doing an activity-specific warmup before sessions - hopefully that's the last of those injuries I'll have to suffer.