Agents shift jobs almost as quickly as actors. Two of the three agents in my current office have changed in the last year. The people who replaced my first agent were not excited by me. So, after six years, I left without getting another agent first. She was freelancing again, but with no protection.
Agents prefer to work with their signed clients first.
I was on the verge of signing with him. After a year, he left. And, as you'll remember, two out of the three agents there now are new, and they don't know me at all. Every time you make a change, you lose ground unless you're really established. You lose your shorthand, your way of talking with a particular agent.