iac: I believe one of the primary reasons Rabbeinu Gershom was motivated to enact the Cherem against a husband unilaterally divorcing his wife against her will was for situations such as you describe. Imagine a wife suddenly suffers from a huge health problem r’l. She is c’v confined to a wheelchair and needs aid to simply move or get up. And it is believed her conditional is permanent and incurable. Or she is now starts suffering from great emotional or mental health difficulties. So the husband then feels he could “do better” and marry a healthy wife after divorcing his now crippled wife. Rabbeinu Gershom made sure she can stop him from doing that and force him to remain married to her.
Similarly the Torah gives the husband the right to decide not to divorce even if his wife demands it. Imagine a husband becomes poor. Until now he was middle class or even wealthy when business went bad and the family is now living in shambles and on shoestrings. The wife is embarrassed by her new financial state. She can do better. So she demands a Get. The Torah says no. He has the legal, moral and ethical halachic grounds to deny her request and insist that the marriage continue.
And in both the above examples the wife and the husband would be correct to deny the divorce request.