Why is the torch held by the Statue of Liberty in its right hand no longer open to visitors?

The Statue of Liberty was damaged during the Black Tom explosion of 1916. This was a German terrorist plot to destroy US-made munitions that were being shipped to allies in World War I. Although the US was ostensibly neutral at that time, due to the British blockade of Germany, only allies were able to buy US made arms. 2,000,000 pounds of small arms and artillery ammunition were stored on Black Tom Island. A fire was lit by conspirators and soon engulfed the depot, leading to multiple explosions of the weapons. Fragments of the explosion struck the Statue of Liberty, mostly damaging the torch-bearing arm. The statue was closed to visitors for repairs, and when it reopened ten days later, the narrow ascent to the torch remained closed and has never re-opened to the public since then.

https://en.wikipedia.org/wiki/Black_Tom_explosion
https://en.wikipedia.org/wiki/Statue_of_Liberty
https://www.nps.gov/stli/planyourvisit/frequently-asked-questions-statue-of-liberty.htm#:~:text=The%20torch%20has%20been%20closed,that%20ascends%20to%20the%20crown.

It was shut down over safety concerns following damage from an explosion and years of deterioration.

In 1916, a number of events led to the closure of the torch's observation platform. On July 30, the "Black Tom" explosion occurred in New York harbor. A group of German agents set out to destroy a collection of United States military goods that were meant to be supplied to the Allies in World War I. The explosion reached as far as Liberty Island and caused some minor damage to the statue's exterior.

On top of the damage from the explosion, the right arm's structure was deteriorating from years of people climbing up and down. Truthfully, it was not meant to sustain that much weight and there were many reports that guests felt it shaking from within. For safety reasons, it was decided to not allow any more guests to the top.

https://www.statueoflibertytour.com/blog/lady-libertys-torch-how-to-see-it-and-why-it-matters/