Why is halacha so strict? I can't answer, as I disagree the premise of this question. I find that the question makes no sense. Let me explain.
The world we live in is governed by both physical and spiritual laws. We are used to the rules of physics — gravity, chemistry, biology, etc. — and accept the way these laws govern our existence. An attempt to violate these laws — such as walking off the side of a building and willfully resisting the force of gravity — will have very grave consequences.
We are less used to the spiritual laws that govern our existence, but they are no less real. Those laws are set down in the Torah and are known collectively as halacha or "Jewish Law." Unlike the laws of physics, the laws of spiritual reality can be willfully (or accidentally) violated, and most of the time such violation results in no visible physical consequences. But it does result in spiritual consequences that are no less real. These consequences can be summarized as increasing one's distance from (or decreasing one's closeness to) G-d. Closeness to G-d is the ultimate pleasure we can ever experience, and estrangement from Him the ultimate misery.
Now in reality, what looks to us as two sets of laws are really two manifestations of one set of law, the rules that Hashem (G-d) put into motion when He created this world. If we could see the world from His point of view — and one day we will — we would understand how these two sets of laws are really just manifestations of His Will.
Now, back to your question. You asked: "Why is the Jewish tradition so strict?"
My answer: "Do you think that the laws of physics are strict? Do you think that the law of gravity is strict? The laws of chemistry?"
So you see, such a question makes no sense. It comes from and is a manifestation of our distance form Hashem. Were we closer to Him, we would be much more cognizant of His Spiritual Law and the consequences of violating that Law — just like we are aware of such in physics.
Is Judaism strict? Not at all. It's real.
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