Because kael's household that time was not really secured. The only member remaining is a child, the only person who's holding the mansion together was uros. On the other hand, the place that was suggested to him has an active members so the household is prosperous.
The bright future of a butler lies with the household they are working at.                                            
                                                I see. Well i think in the pov of a servant, especially of a butler. I think their mindset focuses more on the pride of serving someone than the pay itself.
I often encounter this behavior of butlers where they take pride and joy on who they're serving with. I dont know how to explain it properly but all i can say is they don't think less of themselves as house manager... their bright future is too die or retire SATISFIED with their work and master.
Respectable and competent master = happy butler
Incompetent master = sad butler                                            

		
What’s a bright future for a Butler? In all the stories I read and movies I watched that have butlers, they remain butlers till death or retirement if there is one. So what did she mean by telling Uros that he would have a bright future ahead if becomes a butler elsewhere else?