Sounds like your cricketers are overtraining. During training, rest is a *vital* part of a proper training programme. Overtrain and the body stresses too much and the immune system is hit, making the athlete (whatever the sport) prone to illness, infections, fatigue and generally they will not reach their potential. They may well have a better diet than, ahem, rollies and steamed puddings, but overtraining has its serious downsides.
I know too many (often young) sportsfolk (in cycling mostly) who are great juniors, then get taken on by more serious teams/clubs/coaches and end up seriously ill - even to the extent of glandular fever knocking them for six.
Not that my son is in any danger of overtraining in his cycling ... lazy tyke.
Think of them as battery hens - in a stressed environment, their bodies stressed to produce ever more and what happens? Burn-out, illness...