@synthesis I assume it’s a mitigation for the risk of bashing arms/wrists/hands - but note applicability - last line (scroll down).
Do field sports players wear watches on the field of play?
Rugby players?
World Triathlon Competition Rules
18 January 2025
p49/215
4.11 (Swim)
f.) Illegal Equipment:
(i) Athletes must not use or wear:
<>
● Any jewellery. deemed to be a hazard to themselves or other athletes.
(Athletes may be requested to remove any such items.)
● Watches. This non allowance applies to Elite, U23 and Junior races in Standard and shorter distances.