marriage - Why only 100 zuz to a widow/divorcee?

In a Ketubah, the Rabbis instituted that a man should obligate himself to pay his wife, should he chose to divorce her (or he dies). If she had never been married before, he obligates himself to pay 200 zuz. If she was previously married, he obligates himself to pay 100 zuz. (See Rambam Hilchot Ishut 10:7) [That is the minimum, he could offer more if he wants]

The Bartenura on Mishnayot Peah 8:8, says that 200 zuz is enough to support someone for one year.

If that's the reason the husband promises 200 zuz, why is he only obligated to pay 100 zuz to a widow/divorcee? Why did the Rabbis feel it was enough to support her for only half a year?

If that's not the reason, what is the reason for the discrepancy between a previously unmarried woman, and a previously married woman?

Answer

I'm not sure if I understood this correctly, feel free to point put any mistakes.

The Yad Eliyahu, after much back and forth, seems to say that:

• 
  

  The reason for a monetary obligation is, as the Rambam (Hilchot Ishut 10:7) says, in order to make sure that it should not be of little import for a man to kick his wife out of the house.

  
  


• 
  

  The Rabbis agreed that 100 zuz is enough to ensure this. (even though if a person is wealthy 100 zuz is nothing, this is a substantial sum for a poor person and therefore the Rabbis settled on this sum, so that law would equally apply to everyone)

  
  


• 
  
  

  There is an argument in the Talmud (Ketubot 10A) if the money obligated by the Ketubah is a Biblical or Rabinical Decree. According to the one who says it is Biblical, we learn it out from Exodus 22:15-16, "he shall pay money according to the dowry of virgins.". From Devarim 22:29, we learn that the dowry of virgins is 50 Shekalim.

  
  


• 
  

  [It would appear that everyone agrees that the monetary obligation for a widow etc. is Rabinical, the only discussion is whether the monetary obligation for a virgin is the same]

  
  


• 
  

  However, most agree that (at the very least the amount of) the monetary obligation is Rabinical. The Rabbis who instituted the amount would have settled by 100 for everyone, but because the verse does mention that a virgin's price is 50 Shekalim (200 zuz), the Rabbis made that the monetary obligation for a virgin, leaving the monetary obligation of a widow etc. at the price they already thought was enough.

  
  

See Kobetz Al Yad HaChazaka as well.