WACO, TX: Why didn't baptist preacher Matt Baker simply ask wife Kari Baker for a divorce?

Waco Texas. Minister on trial for his wife’s murder.
The Associated Press reports that the ex mistress of preacher Matt Baker is claiming that he smothered his wife with a pillow to be with her. Vanessa Bulls, the woman at the center of the murder trial, is claiming that Mr. Baker confessed to her during their pillow talk that he drugged his wife with sleeping pills (he led his wife to believe they were sexual enhancement drugs of some sort….Viagra, perhaps) and then when she was groggy, he smothered her to death so that he could be with Vanessa free and clear.
Mr. Baker, in his defense, claims his wife committed suicide and it appears that there is a history of suicide attempts in her not so distant past. But Vanessa claims Baker went out of his way to make it appear that his wife had committed suicide when in fact he killed her so that he could be with Vanessa. True or false? Who knows.  The only thing anyone knows for sure is that the wife, Kari Baker, is dead.
It never ceases to confuse me as to why so many spouses – husbands in particular – would rather kill their wives than ask for a divorce. How does a person protect themselves against something like this happening? Is it a function of equitable distribution? They would rather kill the spouse than share the marital assets? I cannot, for the life of me, understand what is the motivation for these inter-marital murders when it is so easy to tell someone you want out of the marriage. Texas is a no fault state to boot so its not like Mrs. Baker could have prevented her husband from getting the divorce if he was hell bent on getting out of the marriage. So it defies logic. And reason. Assuming that what the mistress Vanessa says is true.