Depleting assets: No matter how good a producing well is, it will eventually stop producing. When this happens, mineral rights will be virtually worthless. It is difficult to predict when a well or field may deplete, many people decide, at some point, to convert some or all of their mineral rights into other assets, which may hold their value longer, and may appreciate more than their dwindling oil and gas interests.
Diversification: if a large portion of your current income is derived from mineral rights, you are much more vulnerable to the wild price swings inherent in the oil and gas industry, which could drastically reduce your income. Selling a portion, or all, of your interest would reduce that risk, allowing you to invest money from the sale in other, more stable, investments.
Estate Management: Often it is easier to liquidate mineral rights held by an individual while they are still living, rather than waiting until after their death. If the individual owns mineral rights in more than one state, their estate would need to be probated in each of them in order for title to pass to their heirs, in most cases. This can result in considerable expense for an estate, and heirs. It is much easier to distribute cash assets to heirs than it is to divide up property after someone has passed.
Fractionalization: As mineral rights are passed down from generation to generation, they are divided into many smaller, fractional amounts, thus lessening their economic value. Keeping track of the mineral at this point can become more of a headache than they are worth to the heirs. This is one of the main reasons owners decide to sell their mineral rights while they are still alive, rather than allowing their in value per fractional split, per generation.
Lump sum payment: A lump sum cash payment can be used more effectively than small monthly royalty checks, and can be used to pay off large bills at once, or used to fund college education, or a retirement account.
Tax advantages: eliminating mineral ownership can significantly simplify your tax returns each year.