Dumbledore was busy with the Triwizard Tournament
The Quidditch World Cup Final wasn't the only big thing happening that year. The Triwizard Tournament was also taking place in Hogwarts. It may not have been so obvious in the movies, but the Tournament was a big deal. The Ministry of Magic itself had a part in planning the Tournament.
The safety of his students is an important charge for a headmaster. The Tournament was importing highly dangerous creatures, and Dumbledore had to take the necessary precautions to protect his - and Beauxbatons's and Durmstrang's - students.
“Oh, and I almost forgot,” Fudge had added. “We’re importing
three foreign dragons and a sphinx for the Triwizard Tournament,
quite routine, but the Department for the Regulation and Control
of Magical Creatures tells me that it’s down in the rule book that
we have to notify you if we’re bringing highly dangerous creatures
into the country.”
The Tournament had not been held for a century, meaning that extra precaution had to be taken to ensure the safety standards were met.
“As I was saying,” he said, smiling at the sea of students before him, all of whom were still gazing transfixed at Mad-Eye Moody, “we are to have the honor of hosting a very exciting event over the coming months, an event that has not been held for over a century. It is my very great pleasure to inform you that the Triwizard Tournament will be taking place at Hogwarts this year.”
“There have been several attempts over the centuries to reinstate the tournament,” Dumbledore continued, “none of which has been very successful. However, our own departments of International Magical Cooperation and Magical Games and Sports have decided the time is ripe for another attempt. We have worked hard over the summer to ensure that this time, no champion will find himself or herself in mortal danger.
Dumbledore had the Tournament to worry about, and Voldemort's Horcruxes as well. He had his hands filled, and therefore had no time to attend the Quidditch World Cup Final.
Given the choice between planning the Tournament's challenges in a way that ensured safety for his students and serving as a "wizard-bodyguard" whilst attending the Cup, he obviously chose to ensure the safety of his students, given that there was already a high-level of security there: comprised of many Ministry wizards and the Minister of Magic himself.
And also, it's probable that Dumbledore didn't even get tickets in the first place.
“I do hope you will allow us to take Harry to the match, as this really is a once-in-a-lifetime opportunity; Britain hasn’t hosted the cup for thirty years, and tickets are extremely hard to come by.”