In the book, it’s never shown to be.
The Room of Requirement is never shown to be accessible by brute force in the books. In the book, neither Umbridge nor Filch ever actually get into the Room of Requirement at all - instead, she catches the students after they leave the room.
“Dobby – this is an order – get back down to the kitchen with the other elves and, if she asks you whether you warned me, lie and say no!’ said Harry. ‘And I forbid you to hurt yourself!’ he added, dropping the elf as he made it over the threshold at last and slammed the door behind him.
‘Thank you, Harry Potter!’ squeaked Dobby, and he streaked off. Harry glanced left and right, the others were all moving so fast he caught only glimpses of flying heels at either end of the corridor before they vanished; he started to run right; there was a boys’ bathroom up ahead, he could pretend he’d been in there all the time if he could just reach it –
Something caught him around the ankles and he fell spectacularly, skidding along on his front for six feet before coming to a halt. Someone behind him was laughing. He rolled over on to his back and saw Malfoy concealed in a niche beneath an ugly dragon-shaped vase.
‘Trip Jinx, Potter!’ he said. ‘Hey, Professor – PROFESSOR! I’ve got one!’
Umbridge came bustling round the far corner, breathless but wearing a delighted smile.”
- Harry Potter and the Order of the Phoenix, Chapter 27 (The Centaur and the Sneak)
Therefore, this seems likely to be just a plot point entirely invented by the movies which isn’t quite consistent with the information given in the books, like the escaped dragon, the burning of the Burrow, and the Dark Lord exploding.