The nationalists could have escaped to the present day Phillippines which is further from the Chinese and would keep them more safe or to any other island but why only Taiwan and also why didn't the Chinese prevent the nationalists from fleeing to Taiwan.
Taiwan was basically a part of China, and under Nationalist control at the time. (The Philippines were a foreign country.) Also,the Nationalist army, while weaker than the Communists, was far stronger than anything the Taiwanese were likely to put up.
Tom Au is right; his answer is the correct answer. I want to add two more data points:
Hainan was closer to Mainland China and would be more difficult to defend against amphibious assault, Taiwan had the advantage of being far enough away that it was difficult for the communists to invade.
Taiwan had another advantage over other islands: It had been economically industrialized somewhat by Japan, as it was a colony between 1895 and the end of world war II.
The premise of the question is false. It's not true that the KMT/ROC "[went] to the island of Taiwan and not to any other island". Rather than choosing to "go to" Taiwan and not any other island, Taiwan merely happens to be the largest island that the ROC still has control of.
The ROC also "went to" many other islands. Or more correctly, the ROC also had control of plenty of other islands besides Taiwan. (Indeed even today, the ROC still has control over at least three groups of islands besides Taiwan: Matsu, Penghu, Kinmen.)
For example, another one of the last bits that the ROC had control of was Hainan, which fully fell to the PRC only in May 1950, 7 months after Mao declared the inception of the PRC.
So I think the question should instead be: "Why did Taiwan (along with some minor islands) not fall to the PRC?"
And the answer would be that in June 1950, the Korean War started. And the US decided to change its previous stance (of not trying too hard to help the ROC) to "drawing the line at" and protecting the "unsinkable aircraft carrier" that was Formosa/Taiwan.
The continued existence of the ROC on Taiwan to this very day depends largely on US protection.
P.S. Some KMT troops did flee to Burma (and prove an annoyance there for some time).