Float Pool

So I was just recently hired as a float pool nurse for two different departments. Both departments I have experience in but only one of them I consider myself an expert meaning that I haven been consistently working in that department for several years at at time. When I interviewed I was under the impression that I would be floating to both departments on a regular basis but as time went on I see that one of the departments that I float to is chronically understaff meaning that everyday they are short at least 3-6 nurses. The other department that I can float too tends to be well staffed and rarely ever needs an additional nurse.  I am a little disappointed because I was looking forward to being an active member of both units. however I can see clearly that won't be the case anytime soon. My question is why would a company hire me to be a float pool nurse if they knew that I would hardly ever float to the other department? The chronically understaffed department has a high turnover rate also. Why didn't they just hire a nurse to work primarily in that unit. I kinda feel deceived. It's also making me feel like leaving the job and going elsewhere.