"Why?"
Better economics as you demonstrate your continued success
Better capital availability again as you demonstrate success
You're building a future at their expense
There may be a permanent relationship down the road
You learn to play well with others
Technology and resources may already be in place
Family offices are often hungry for talent as few consider them
No risk sharing other than your time, which is not an irrelevant cost
They generally recruit from the professionals who cover them and those can be very expensive hires - so you may come in cheap
Engaging with other professionals
Getting in the door can be difficult - generally less likely to buy performance reports and more inclined to hire people
Singapore, San Francisco, and Zurich are the centers of the FO world