1) It must be that it was a fairly widespread problem because we have a rule (see Beitzah 2b) that the Sages do not make a decree for something which is uncommon ("Lo Shachi'ach"). Even though the idea of the Kesuvah is not exactly a decree but rather a Rabbinical institution, no doubt the same logic applies: Chazal did not introduce such a vast Halachah about something which is anyway uncommon.

2) Furthermore, the Din of Kesuvah is considered one of the great achievements of Shimon ben Shetach, who himself was one of the greatest of the scholars of the Mishnah. The Gemara in Shabbos 14b, when it lists the different Halachos enacted by the early Tana'im, mentions Kesuvah as one of the two great works of Shimon ben Shetach, so it is unlikely that this Halachah would be on an uncommon or unusual side issue.

3) Furthermore, we find another instance of encouragement needed in order to make sure that women would agree to marry. This is in the Gemara later, 84a. The Mishnah there states that if somebody died and different relatives had claims on money that was owed to the deceased during his lifetime, the opinion of Rebbi Tarfon is that the money is given to the weakest claimant. Rebbi Yochanan in the Gemara (end of 84a) explains that the "weakest" refers to the Kesuvah owed to the wife because it is necessary to encourage "grace." Rashi writes that this means that we are concerned that men should find grace, or favor, in the eyes of the women so that the women will be willing to marry them and not be worried that they will lose their Kesuvah at some later time. Again we see that it was necessary to introduce special Halachos to deal with the phenomenon that the women did not want to get married, so it must have been a fairly common problem.

Kol Tuv,

Dovid Bloom