I think this situation has to do with the lack of vision or a goal. They feel the inner need to practice but it's difficult for them to get excited enough about some pieces and so they practice but don't see a lot of progress in return.
Obviously, the choice of the music can be wrong for their current technical abilities, or practicing habits have been incorrect. At any rate they really don't see themselves going anywhere in organ playing as time goes. That's why their efforts are inconsistent, too.
In some cases, this kind of practice can lead to quitting organ playing altogether. Because what's the point of playing the organ, if you don't have a vision or a dream of what you want to accomplish in the future? So at some point the efforts of pushing ourselves during practice and playing with determination and focus disappear and an organist might give up playing this instrument in the long run.
If you struggle with inconsistent efforts, my advice would be to get really focused about what you want to achieve in playing the organ. Set exciting yet realistic goals.
A goal is not a goal if it doesn't have a definite date on it. So write down your goals on a separate sheet of paper and set a date of when you want to meet your goal. Then you have to think about the plan of how to achieve it. And don't forget the importance of writing down the daily steps, too.
My final advice would be to surround yourself with positive people you can trust who can support your efforts. It can be a fellow organist or a few friends who might appreciate what you are doing or a mentor/coach. Sometimes your family members can't provide such support and leadership.
This way if you can talk regularly about the progress of your practice, you will not feel alone on this mission and you will be more likely to stay on track with your plan of action and daily steps which will prevent inconsistent efforts to appear in your practice.