Minimum Switching Frequencies in Boost Converters
Two reasons...


Higher frequencies means you can use smaller, cheaper and lighter components.
Under a certain frequency (about 50KHz) audible noise is generated. At the higher end it will drive your pets nuts, lower it will drive you and your users nuts.


The trick is to come to a balance. Make the frequency high enough to limit the costs while low enough to be able to find suitable switches that are not too lossy. 

There is also another trade-off. Lower frequencies means more ripple you need to deal with, but then again high frequencies means more EMI noise. 

Getting the right balance is a bit of an art.