Question

Why did otzi remain intact

Answer 1

If you meant How he stayed intact.

It was a chain of extraordinary coincidences:
Ötzi died high above in the perpetually cold glacier region, where he remained lying in a protective rock gully.
The mummi cation process began and with the onset of winter, snow covered the dead body – now he lay deep-frozen as if in a freezer compartment.

Answer 2

Otzi is a mummy of a man who lived in the Otztal Alps, on the border between Austria and Italy. Otzi lived between 3,400 and 3,100 BCE, making him Europe's oldest known natural human mummy. Otzi died in a glacier region, and this allowed his body to remain protected by the ice that surrounded him, as in a freezer. This is why Otzi remained intact for so long.