Why does it seem appropriate for Capulet to personify death in act 4, scene 5 of the play? You may want to consider why, in the larger context, people personify death; is it a coping mechanism? What is it about making it into a person?

In Romeo and Juliet, death is personified at several points and by several characters. Lord Capulet addresses Death with the literary device of apostrophe, and he personifies death as well. His words call attention to the utter powerlessness he feels at not being able to help his daughter; Death has all the power. Paradoxically, he says he cannot speak, perhaps indicating his confused state. Further, as he does not yet know the circumstances of her death (although at that point she was still alive), he has no one to blame. Ironically, Romeo is the cause of her demise, so calling Death his “son-in-law” is appropriate.
Capulet’s words are also appropriate in the context of William Shakespeare’s usage at other points. When Juliet threatens to kill herself, she says, “Death, not Romeo, take my maidenhead!” The next day, at Juliet’s tomb, Romeo personifies death as he beholds her lifeless body: “Death, that hath sucked the honey of thy breath . . .” He continues, comparing Death to a lover, thus continuing the comparisons in the previous scenes.

Shall I believe
That unsubstantial Death is amorous,
And that the lean abhorred monster keeps
Thee here in dark to be his paramour?
https://myshakespeare.com/romeo-and-juliet/act-5-scene-2

In Act IV Scene V of Romeo and Juliet, Capulet personifies death as he looks at his daughter's lifeless body. Capulet talks about death being his "son-in-law," for example, and "his heir." For Capulet, death is like a groom who has taken Juliet away and made her his bride.
By personifying death in this way, Capulet emphasizes the untimely and unexpected nature of Juliet's death. Remember that Juliet is only a teenager and was due to marry Paris, beginning a new chapter in her life. For Capulet, then, death has taken Juliet before her time, and his personification of death reflects this idea.
In addition, Capulet personifies death to emphasize his grief. As we see from the text, Capulet is devastated to find his daughter dead and struggles to find the words to express his sense of loss. This is clearly shown in the following line when Capulet blames death for his inability to express these feelings:

Death, that hath ta'en her hence to make me wail,
Ties up my tongue and will not let me speak.