I don't think the game needs to simulate everything in real world, because this is impossible. No matter how realistic the game is, some elements cannot be fully simulated.
I don't prefer only changing this part to help some managers who do not properly manage players' conditions, but I don't fully object trying to simulate more aspects of pre-season on first season day. I may love to see even more changes at the same time. For example, morale of most players are set to full except those who may worry about future (have not yet signed contracts or are still injured at season beginning), healthy players' conditions may start at about 50% (so they need 1 more day to become fully fit), all injury out-of-action periods reduce by about 8 days, players can recover condition and from injuries even if they have not yet signed new contract, etc.