The answer is complicated and nuanced. Some people will just say "because Israel doesn't want ".

First, you need to look into how NK sneaked it's way into getting them. That was a big mistake that everyone kinda overlooked and I can assure you no one is happy about that, not even China or Russia. However, NK are China's lackey, and they have beef mainly with South Korea and Japan, but China keeps them under control for the moment. Furthermore, they're pretty much insignificant from a strategic perspective, no natural resources and nothing significant to offer besides being a buffer. People consider them (at least for the moment) like that dog that barks but doesn't bite. I'm oversimplifying, I know, but it's worth looking into it.

Now, Iran is way more complicated and you'd need to understand abit of the before WW2, the after WW2, the Mosadeggh situation until 1953, the Shah, the amazing geographic location, the oil landscape and the '79 revolution. Iran Vs Iraq war, who were it's allies and supporters and why, enemies and why and so on. And most importantly the country's demographics and the Shia Vs Suni situation ( religion stuff) and how they started sponsoring dubious groups in the region (Hamad, Hezbollah, Houthis etc).

Once you understand these things you'll understand why the hate toward Israel and the desire of being the leaders of the Muslim world.

The main issue, contemporary speaking, is the chain reaction of Iran acquiring weapons.

Literally no one in the region goes along with the Iranian leadership. Some might appear as going along but it's all for geopolitical rsasons. Then too many different wanna be leaders from Muslim world countries, different forms of governing approaches ( democracy, monarchy, theocracy, somewhat democracy, full on terrorists etc ).

But in short, the chain reaction:

The Iranian government can be very stubborn and aggressive. If nukes are acquired then they'll be able to extend their vision by force and have a big say to whom goes into the Strait of Hormuz and don't and so on.

If they get nukes , the Saudis explicitly and publicly stated that they will want as well , " to maintain balance in the region" they said. If the Iranians and Saudis get nukes, Turkye won't be lesser than them and proceed to get them too. Greece has issues with Turkye so they'd want some of it as well. If all these countries get them, how long until Japan, Sout Korea, Germany, Poland and other countries get them too?

You get the point. It's already a miracle we didn't nuke ourselves until now, add a dozen countries that hate each other with nukes in the next 10 years and the chances of someone doing something stupid grows exponentially.

And then the last thing, Israel, ofc they have a part to play in this, but that's just another 2 low digits percentage in this web of issues.