The Big-League teams are already playing games at the training camps in Florida and Arizona.
Players essentially report one day and play a game the next. In the old days, the routine was very different. The ball club owned the facility in many cases, underwrote the costs and didn’t worry about the expenses all that much. The ball players eased into their workout routine. Now they report ready to compete. (Originally spring training was designed for players to dry out after a winter of hard drinking.)
With the escalating salaries that came about, bringing about millionaires out of half or more of each team, there was a move to make spring training a profit center.