Quite often though you don't have a choice about learning another art if you want to stay in martial arts. If you move around a lot ie in the military or your club closes down you don't always have the choice of staying in the same style. My instructor has a few black belts because he was in the army for over twenty years and did whatever style was available to him wherever in the world he was. I have two because my first club closed down when the local council sold the gym to a private company for flats and I couldn't travel at the time.
The moving around thing is one reason we don't ask children to change their belts to white when they join us after moving here, they are only going to be with us two to three years and some of the children have already been to a couple of different clubs, it's very discouraging to always go back to white belt every time they move, bad enough changing schools and friends. If they want to grade with us they can, they start at the beginning and earn our belts but only change when they go pass their original belt ( they do get one of our belts and a certificate though). Sounds confusing I know but service children have enough going on in their lives without any hassle from something they should enjoy doing. We have a very broad curriculum so nobody feels left out! We aim that whatever club they go to next won't be too strange, we teach the various ways you can bow, the various fighting stances, instructions in Japanese, English and Korean and anything else that's interesting. The children have a folder where they collect information, pictures etc about all the different martial arts.
One of the children, a teenage boy was close to his Shotokan brown belt so our instructor whose karate style is Shotokan taught him and graded him up, the lad joined the army, his father's regiment, and gained his black, Two years later he was killed in Afghan, he was only twenty one. ( we also lost one of our MMA students just twenty, out there) All our child students know someone who was killed or injured in Afghan, so if our style of teaching, grading and whatever upsets some because it's not 'pure', to be honest we really don't care.