Why were there no Hogwarts Quidditch games in Goblet of Fire? Was there an official explanation from Dumbledore that the school games are cancelled due to Triwizard tournament and if so, why?
There was an official explanation, at the beginning of the year, that there was no Quidditch house cup. Dumbledore gave this announcement in the welcome speech at the beginning of the year:
'It is also my painful duty to inform you that the inter-house Quidditch Cup will not take place this year.' 'This is due to an event that will be starting in October, and continuing throughout the school year, taking up much of the teachers' time and energy - but I am sure you will all enjoy it immensely.'
(The event is the Triwizard Tournament, obviously).
Dumbledore announced that there would be no Quidditch over the year, just before announcing the Tri-Wizard Tournament.
Towards the end of the book we see the real reason for the cancellation of Quidditch:
The final challenge is a maze that has been grown on the Quidditch pitch.
From a writing point of view, I guess with all the action of the tournament, fitting in Quidditch matches would have been a bit too much.
The unofficial reason is that JKR found it difficult to do something new in the Quidditch matches every book . Reading about a fast-paced game is not exciting, after all. So, she used various reasons in the later books to reduce the number of matches.
I've noticed that there has been a description of a maximum of one Quidditch match in every book (save, The Deathly Hallows -which had none).
So,owing to the description of The Quidditch World Cup, a Hogwarts Quidditch match in addition to this would have been unlikely.
"Much to Harry's disappointment, the inter-house quidditch cup didn't take place, as the students from Beauxbatons and Durmstrang were coming for the Triwizard tournament."