Because Saturday 3PM premier league games are banned from being shown, on British Television, as it is believed that they will interfere with crowds at lower league games.
In theory, if a football fan has the choice of watching their local team, in the cold, and wet, or watching a premier league game, especially one featuring a team they might also support, either at home, or in the pub, then many will choose to watch the televised game, and smaller, lower league, teams, will lose attendance, and finance, thus they could go out of business.
Televised games, at other times, are not deemed to interfere with the lower leagues, and so are acceptable, to everyone except Sky, and now BT, as they want the monopoly on showing EPL games, at an over inflated subscription, in order to recoup the money they have to pay, for the EPL games they show.