Plony only comes up once in all of the Sifrei Tanakh and is spit upon by his late brother's wife. He also loses a shoe. (Read all the details in Ruth Chapter 4.) Did our ancestors have no respect for men who were recently divorced (literally, "Plony, the one who pays alimony") or are we expected to move on from failed marriages and the death of our brother so quickly, as far as marrying his wife?
Courtesy of my brother
Important correction: Ploni isn't described as Machlon and Chelyon's brother. Per p'shat Tanach, we do not know what his relationship to them was. The gemara in Bava Batra 91a however states that he was their uncle (Elimelech's brother). This is important because it means that he most likely wasn't halachically grieving at the time, since Avimelech passed away some time prior (Ruth 1:3-4).
As for the point of his failed marriage - well, the Torah if I remember correctly only brings two possible reasons for divorcing, and that's if a man doesn't like something his wife does (Devarim 24:1):
"When a man taketh a wife, and marrieth her, then it cometh to pass, if she find no favour in his eyes, because he hath found some unseemly thing in her, that he writeth her a bill of divorcement, and giveth it in her hand, and sendeth her out of his house"
or he hates her (Ibid. 3):
"and the latter husband hateth her, and writeth her a bill of divorcement, and giveth it in her hand, and sendeth her out of his house..."
So it seems that Ploni didn't really have a good reason not to marry Ruth: He wasn't grieving and though he was divorced, he would have only been all too happy to be rid of his first wife. He should have celebrated the divorce, it being a mitzvah, by making another (one mitzvah leads to another): Marrying his nephew's wife in a levirate marriage.
Besides, he was from the Tribe of Yehudah. Yehudah expected his son Onan to marry Tamar in a levirate marriage a short time after Er's death (the passage of a long time is only stated after Onan's death - Beresheet 38:12). It was incumbent upon Ploni to follow up on the family legacy and marry Ruth, even if he was grieving (though he likely wasn't).
