And I beseech you, good master secretary, pray my lord my father and my lady to be so good to us, and to let me have their blessings and my husband their good will; and I will never desire more of them. Also, I pray you, desire my lord of Norfolk and my lord my brother to be good to us. I dare not write to them, they are so cruel against us; but if, with any pain that I could take with my life, I might win their good wills, I promise you there is no child living would venture more than I.

So that’s an excerpt from her letter to Thomas Cromwell after she was banished from court for marrying without permission.

My impression from this is that her male relatives were not especially kind to her. Bearing that in my mind, I tend to think that she made the decision to marry someone before a husband could be chosen for her by her father, brother, uncle etc. 

Because her marriage prospects could only have gotten better/wealthier, not worse, after she was officially the Queen’s sister (she was unmarried for a few years after Carey died), I don’t think wealth was enough of an incentive. 

“Carey died greatly in debt” (? according to Wiki)…Mary sold Anne a piece of her jewelery after Carey’s death (Henry gifted Anne the money to buy it, we know this because there’s an account of it in his Privy Purse expenses) so that could very well be. It’s also possible the marriage wasn’t a love match, and Mary didn’t want a similar one arranged that was based on lineage ( Carey was the third cousin of Henry VIII).