Why do the founders of dynasties generally experience a major power reshuffle after their death?

Power recognizes people, not chairs.
The founding emperor sits in that chair because he personally carved and built it.
The ministers follow him not because he is emperor, but because he is the big brother. The big brother is alive, sharing wealth and land, everyone listens to him—that's personalized authority.
When the big brother dies, his son takes the throne.
Who is the son? In the ministers' eyes, he's just a young man who hasn't carried a gun or shed blood.
You say you're emperor, and the chair is passed to you, but the deterrent power around the chair isn't inherited.
At this point, a deadlock appears: the son holds the crown but can't control the situation; the ministers hold military power and experience but can't openly oppose him.
Both sides feel awkward. What to do? They can only reshuffle.
The son thinks: these elders don't accept me, I need to replace them with my own people.
The ministers think: this kid's foundation isn't solid; rather than waiting for him to act, it's better to strike first.
The maternal relatives think: taking advantage of the chaos, push the empress dowager up, and half of the world will be ours.
So-called "major power reshuffle" is not some conspiracy theory, nor purely human greed—it's simply an inevitable friction period when power changes hands.
The old emperor is there, acting as a stabilizer, capable of handling any voltage.
When the old emperor is gone, the stabilizer is gone, and the original wiring must be reconnected.
During this process, circuit breakers trip, short circuits occur, and some components burn out—that's perfectly normal.
As for whether the casualties during the power outage are meritorious officials, princes, or common people—that depends on each dynasty's skills and luck.
Ultimately, power is never that jade seal or that chair.
Power is a relationship between people.
When the most critical person in that relationship leaves, everyone else must find their new position.
That's what reshuffling means.