Kesuba's purpose is to prevent divorce not to provide financial security

In the previous post about pitzu'im (divorce settlement) it was asserted or implied by various commentators that the kesuba was instituted to provide financial security for the wife in case of divorce. In fact, the sources I have seen give it no such role. According to the Talmud (Kesubas 11a) the kesuba was instituted to make divorce difficult - for both the husband and wife. It is viewed as a device of social control over marriage. A rebellious wife loses her kesuba. A rebellious husband must add to the kesuba. There is mention in the Talmud of major rabbis who didn't divorce a difficult spouse simply because they couldn't afford to pay the kesuba. The focus of rabbinic concern was solely to create pressure that the couple remained married - not that the wife shouldn't be penniless if she was divorced. The fear was that a woman might fall in love with another man and want to leave the marriage. The loss of her kesuba was motivation not to focus on being in love but to have a stable marriage. If she declared that she found her husband disgusting and wanted out of the marriage - the divorce was only given if she accepted the loss of her kesuba and the husband agreed to the divorce. Permanence of marriage not personal happiness is clearly the main concern of the Rabbis. In fact I don't know of any rabbinic sources regarding the financial security of the divorced wife until recent times when the issue of pitzu'im (divorce settlement) was raised. Today there is concern - in the secular justice system - for a variety of payments to ensure that the wife is not penniless and that she get an equitable share of the couple's wealth as well as child support. This modern secular concern clashes with halacha. Any sources to the contrary would be greatly appreciated.

Justice Menchem Elon states the following in Principles of Jewish Law

The ketubbah was instituted for the purpose of protecting the woman, "so that he shall not regard it as easy to divorce her" (Ket. 11 a; Yev. 89a; Maim. Ishut 10:7), i.e., in order to render it difficult for the husband to divorce his wife by obliging him to pay her, in the event of a divorce, the sum mentioned in the ketubbah, which generally exceeded the sum due to her according to law. As this is the object of the ketubbah, some auth­orities are of the opinion that since the herem of Rabbenu Gershom, which prohibited the divorce of a wife against her will, the same object is achieved in any event; it is therefore argued - on the analogy of Ketubbot 54a concerning the ravished woman who is thereafter married by her ravisher and, according to pentateuchal law, cannot be divorced - that there is no longer any need for a ketubbah to be written. However it has remained the halakhah that a ketubbah is to be written (Rema EH 66:3, concl.).

Rabbis Broyde and Reiss have a good article on  JLaw

[...] the purpose of the ketubah was to mandate payments in cases of divorce high enough so that a man would not hastily divorce his wife. Payments of $25, $100, or even $1,000 hardly accomplish this talmudic mandate. Consistent with this notion, it is noteworthy that Rabbi Feinstein dismissed the European practice which was to evaluate the ketubah at 75 rubles because this sum would be laughably small nowadays.

What then is the purpose of the Ketubah in cases of divorce after the ban on polygamy and unilateral no-fault divorce? Rabbi Moshe Isserless (Ramo) provides a very important answer.

He states in the beginning of his discussion of the laws of ketubah:

See Shulchan Aruch Even Haezer 177:3 where it states  that in a situation where one only may divorce with the consent of the woman, one does not need a ketubah. Thus, nowadays, in our countries, where we do not divorce against the will of the wife because of the ban of Rabbenu Gershom, as explained in Even Haezer 119, it is possible to be lenient and not write a ketubah at all; but this is not the custom and one should not change it

[...]

However, no one argues with the basic economic assertion of the Ramo: The purpose of the Ketubah written to impose a cost on the husband for divorce — so that he should not divorce her rashly — has become moot; this basic purpose has been overtaken by the ban of Rabbenu Gershom which simply prohibited that which the Talmudic Sages sought to discourage. The ketubah neither establishes nor effects nor modifies any economic rights in cases of divorce without fault in places where Cherem deRabbenu Gershom is accepted. In situations where Cherem deRabbenu Gershom is not applicable due to misconduct, fault is always found, and no ketubah payment is thus mandated by Jewish law.

Rav Moshe Feinstein (Igros  Moshe E. H. 4:91): The value of the ketubah is not known to rabbis and decisors of Jewish law, or rabbinical court judges; indeed we have not examined this matter intensely as for all matter of divorce it has no practical ramifications, since it is impossible for the man to divorce against the will of the woman, [the economics of] divorce are dependent on who desires to be divorce, and who thus provides a large sum of money as they wish to give or receive a divorce.