You can get a lot of things by doing something to earn money, then using the money to buy the thing. One large exception to this is things in the very near future, since the process of earning money and spending it takes some time. So one big reason for being disinterested in earning money would be that you have a very short term focus.
The usual reason people give for being disinterested in money is nearly the opposite: that they are inordinately interested in big, important, deep things and thus have no need for such a petty mundane thing as money. Money is presumably useful in seeking such big goals, since it can at least buy you out of other mundane concerns. But let’s suppose these people are right, and money is less important than usual in this realm, for instance because there are other inputs to deep important goals, that money can’t buy.
Then we should expect people who are especially disinterested in money to be well represented at both the ‘very near goals’ and the ‘very far goals’ ends of the spectrum. My observations of humans suggest at least as many would be at the near end as at the far end. However almost everyone who isn’t very motivated to earn money seems to cite being at the far end as reason for disinterest. Should we believe them?