They do a lot of promotional and charity work on their off-days during the regular season as well.
I have to laugh at people who think a ballplayers season is easy. It is not nearly as easy as they think.
First of all they dont work just a few hours a day. They have to get to the ballpark around 3pm or so, take BP, take fielding practice....etc. Then its gametime around 7pm, games usually last between 2.5 to 3.5 hours (obviously longer if it goes extra innings), then after the game sometimes interviews, showering....etc. By the time they leave the ballpark its around 11pm or midnight.
So their workday is between 3pm and midnight. Thats around 8 to 9 hours, which is what regular people work as well.
Now try doing that 6 days a week. It gets tiring