The real story from The Beatles Bible:
There was a big talk at Candlestick Park that this had got to end. At that San Francisco gig it seemed that this could possibly be the last time, but I never felt 100% certain till we got back to London. John wanted to give up more than the others. He said that he'd had enough.
The Park's capacity was 42,500, but only 25,000 tickets were sold, leaving large sections of unsold seats. Fans paid between $4.50 and $6.50 for tickets, and The Beatles' fee was around $90,000. The show's promoter was local company Tempo Productions.
The Beatles took 65% of the gross, the city of San Francisco took 15% of paid admissions and were given 50 free tickets. This arrangement, coupled with low ticket sales and other unexpected expenses resulted in a financial loss for Tempo Productions...The stage was located just behind second base on the field, and was five feet high and surrounded by a six-foot high wire fence.