Everything has a context. The reason you would file an I-864 with no income or assets is that the petitioner is required to do so in that circumstance. In such a case, a joint sponsor would be required. In the OP's situation, they clearly qualify, and the home equity would be considered within its context as part of the totality of circumstances.
By your logic marriages fail often, so why would anybody try it? Qualifying as sponsor using assets is allowed. It requires properly completed affidavit and properly documented qualifying assets. Anything marginal is risky, but those will clearly qualifying finances are routinely successful using assets to sponsor an immigrant.