Yes, chemistry is a thing, but it figures more in initial stages of attraction.
A good marriage over many decades requires commitment and unselfish love in action.
Fireworks, chemistry, and all of that can come and go - especially when someone gets sick, when tragedy strikes, during lean years, and so on.
We have to remember that with all scripture has to say about the permanence of marriage...that they were talking about
arranged marriages. Almost all were arranged marriages. When scripture says, "Therefore a man leaves his parents and cleaves to his wife and the two become one flesh," and when it says, "Husband, love your wife" and when it says, "Wife, respect your husband," it's talking about an arranged marriage.
May your fountain be blessed, and may you rejoice in the wife of your youth.-- Proverbs 5
You ask, "Why?" It is because the LORD is the witness between you and the wife of your youth.... So be on your guard, and do not be unfaithful to the wife of your youth. --Malachi 2
"The wife of your youth" is the man's first marriage--the one arranged by his parents. Later, as he gained the means, he might contract his own additional marriages with younger women of his own choice and decision.
But "the wife of his youth" was the wife that his parents arranged for him, and God demands he remain with her--and more, that she be the wife who pleases him.
What this means is that God expects any spirit-filled Christian man to be a pleasing husband to any spirit-filled Christian woman, and vice versa.
We in the modern Western world have for maybe the last 70-100 years been using the worst matchmaking system there could possibly by: Sheer dumb luck that one day we will just stumble into "The One" on the street or in a bar or in a classroom, and his "The One" will coincide with her "The One." Absolute chance: That's basically as stupid as stupid can be. Hiring a matchmaker like they did hundreds of years ago is more logical than that.
But it doesn't matter. Even if we use a computer to select for us the perfectly compatible mate, the fact is that humans change. We always change. So in three years, or five, or certainly ten years, a woman will look at her husband and realize, "That's not the man I married." And he won't be. Nor will she still be the woman he married.
And in that moment, they will be in exactly the same situation as a marriage that had been arranged from the beginning. They will have to make a deliberate decision to stay together and grow together--instead of continuing to grow apart.
Unless they have been smart all along and obedient to the instruction of scripture. In that case, they will have been deliberate from the beginning in making conscious decisions to grow together. They will have deliberately made themselves partners in the Project of Life from the start.