That's because the business owner wanted stability and predictability. He needed somebody to go and fix that server when it crashes due to an update, or to add

That's because the business owner wanted stability and predictability. He needed somebody to go and fix that server when it crashes due to an update, or to add a new column to the database when the customers request it, at the lowest price possible. The dev needed peace of mind and job security. To do as little work/thinking as possible at the stable pay. They kinda found each other and it was working just fine for both of them. Then you came into play, bringing more work to the dev at the same pay, if he agreed with you. Had the company owner taken your side, he would likely lose the senior dev, and lose you in a couple of months once you get everything working and decide to move on (I doubt you would be happy with the kind of work the previous dev was doing).