Why do sprinters typically land on the forefoot rather than the heel at high speed?

Answer: It helps the ankle and tendons handle rapid spring-like push-offs

It keeps the calf muscles relaxed throughout each step — The calf muscles are active during sprinting rather than staying relaxed. Together with the Achilles tendon they help control loading and produce a rapid push-off.

It helps the ankle and tendons handle rapid spring-like push-offs ✓ — Forefoot contact suits the rapid ankle loading and push-off used in sprinting. The Achilles tendon can store and return elastic energy while calf muscles produce force, but that does not make forefoot striking universally more economical at every running speed.

It makes each stride as long as possible regardless of braking — Reaching for the longest possible stride can put the foot too far ahead and increase braking. Sprinting depends on effective force and timing, not simply maximizing step length.