I don't think that it was an actual requirement for entry, but certainly a requirement to be accepted in a team. The riders were on their own, repairs and maintenance had to be carried out with what tools and parts were carried on the bike, no helpers allowed. Access to other spares would only be available at the end of the day, with riders carrying out repairs themselves in parc ferme. Quite a few components were officially sealed before the start, a broken seal meant immediate disqualification.
Riders needed to know their tools and be mechanically minded, they wouldn't have stood a chance otherwise. Quick repairs and maintenance were part of the competition.
piet