I'm a simple man and I think simply. Here are possible Dershowitz motives for his interactions with these two scumbags.
Epstein: Dershowitz is a physically ugly and weak man. A nerd, and has been all his life. Without fame and fortune, he would have no chance at sex or a relationship with a beautiful woman. People like him are social climbers and they will attach themselves to anybody that will facilitate their social status and access to power, money, and women.
He, and people like him, are perfect targets for the Espteins of the world. Epstein himself is not power. He is access to power. A facilitator. And once Dershowitz was compromised by Epstein related activities, he became controlled and owned by the real powers.
Lynn Rothschild. Chicken or the egg. Did Rothstein use Epstien to control Dershowitz or did he come to her attention once he was an Epstein property. It depends on how useful Rothschild thought Dershowitz could be to the cause. I think he has been very useful to them. He helps shape opinion by pretending to support conservative causes.
Anyway. That is the story of Alan Dershowitz, as told by Bagster, student of human behavior.
People's motives are really very simple when you stop and think about it. Money, Power, Fame, Sex. Not necessarily in that order.
The weak and ugly are most susceptible to these forces. If you don't believe me, check out the Democrat party and all left wingers in general.
Science.