Presidential Baseball Famous Firsts by Baseball Almanac
In the above link, you can find a mixing use of tenses to decribe a series of historical events:
08-30-1865 President Andrew Johnson brought the first organized baseball team (referred to as "a delegation of the National Base Ball Club) to the White House / Presidential Mansion for a visit.
06-26-1869 President Ulysses S. Grant brought the first professional team (all members of the Cincinnati Red Stockings were paid ballplayers) to the White House / Presidential Mansion for a visit.
04-13-1883 President Chester A. Arthur brought the first Major League team (National League's Cleveland Forest Citys) to the White House / Executive Mansion.
06-06-1892 President Benjamin Harrison is the first U.S. President to attend a Major League baseball game AND the first sitting President to see an extra inning game as the contest remains undecided until the eleventh inning.
06-25-1892 President Benjamin Harrison attends his second game and becomes the first U.S. President to attend two Major League baseball games while in office.
04-19-1897 The Washington Senators are greeted in the Oval Office by President William McKinley who threw out first pitch as Governor of Ohio. The manager of Columbus is now the Senators manager and the first invitation to throw out the first season opener pitch occurs.
My question is: why did the writer use present tense for certain events, and past tense for others? Thank you.
Yes, the present simple tense is sometimes used to talk about past events. It is used to make something that happened in the past more vivid and exciting, almost as if past events are unfolding before our eyes right now. It's quite common in journalism for this reason and is the norm in headlines, partly also because it takes up fewer words and every word counts in a headline (compare 'CHELSEA WIN PREMIERSHIP' with 'CHELSEA HAVE WON PREMIERSHIP'). It's also used in casual speech, for example when recounting something that happened to you recently - you might well place the event in the past and then switch to the present.
"You won't believe what happened yesterday! I was at the pub propping up the bar, as usual, when this bloke - a total stranger - marches upto me and starts jabbing me in the chest, saying ..."
'12 April, 1945. Following the death of President Roosevelt, Harry Truman is sworn in as the 33rd President of the US. Soon after, the war in Europe is brought to an end. Fighting continues in the Far East ...'