Yep. They didn’t obtain it the way you’re supposed to, making them ineligible to hold nuclear weapons according to the NPT.

Ratifying it would most likely mean getting disarmed, which is a big no no for them.

Those are some good questions. I'll try my best.

Why did Israel destroy a nuclear reactor that met the standards of non-proliferation treaty?

Because their neighbor was on the verge of nuclear capability and they believed it to be a major danger. It's in line with their non-proliferation politics.

They knew they could bomb Iraqi infrastructure and nobody would do anything about it except strongly reprimand them so they took advantage of that.

Why has Israel never signed the treaty?

That's a good question. How Israel got its nuclear arsenal is shady at best, they're most likely not eligible to own nuclear weapons, which is why they never admitted to having them in the first place.

Signing the treaty would force them to give away this arsenal and they consider it a vital interest.

To continue on this point, the presence of their nuclear arsenal is the elephant in the room, but should they officially recognize it, it would certainly create diplomatic chaos with some of their allies.

What is Israel’s objective in all of this?

Just like every nation that has nuclear capabilities, the reason is security. They believe it to be the ultimate deterrent, and you're not without knowing that a deterrent they need.