Because he thinks he’ll win by rigging, cheating:
“Trump faces questions about getting out-worked by Harris
Since the Republican National Convention concluded July 18, #Trump has held five campaign rallies.
#Harris will hold that many this week alone.
Democrats & Harris campaign aides have reveled in the contrast in schedules, using it to stoke questions about Trump’s stamina and taunt him with Harris’s large, enthusiastic crowds”
https://apple.news/AS8CnJE2AQOyKwF2bCDZfGA