I have known several music people that will only play music on the black, meaning Eb, Ab, Gb, Db. They cannot fathom extending themselves out to playing something outside of this realm. Why do they do this? It all started out because it was 1) Playing on just the black keys is an easier way to start off sounding good. 2) We learn by rote. Many have gone down this path before us... 3) We tend to play in the style and ways that those around us push us to play in.
A rock keyboard player will be stronger in the guitar keys of E, A, B etc.. because he plays in those keys all the time.. A gospel player is stronger in the flatted versions of those keys.
When we start to look at hand position, there is a HUGE comfort level to consider. Muscle memory comes into play and so does knowing your musical theory. Making the jump to play in keys that you are unfamiliar with is not simply diving in and hacking away at a piece of wood. You have to approach each new key with a plan. You have to look at how the voicings will work together and how you will interconnect the song to make the song into MUSIC. It is not merely mimicking the original key's tune into another tonal center, it is recreating it in another tonal COLOR.
Eb Major does not have the same tonal sound as B major. D Major does not remotely sound like Ab Major. Each tonal center has it's own sound COLOR. We have to take this into consideration when we take about transposition otherwise you can take an otherwise light sounding melody and make it sound heavy and dreary because all you really did was mimic your voicing instead of making your voicing key specific.
In Jazz, we get this a lot. You cannot voice lead the same way once you change the keys of a song because the song is either darker or lighter sounding. Ask yourself this. When you want to change the keys of a song during worship to add energy, do you go up in the key or down? If you answered up, you are correct. Linearly shifting the key up adds energy, you should also look at how you are voicing your chords. That could also add energy... or maybe you are taking it away by merely mimicking?
Just some things to think about