Understanding the deep structure of matter is necessary for two things - materials science and energy science - both of which could have massive economic payoffs for society.
In the modern world, much of our economic growth is driven by innovation - new scientific understandings result in new technologies that result in new products and services that introduce new capabilities into the world that never existed before, and which are in demand because they improve people's lives.
Scaling production and volume lowers prices making them more accessible to everyone. That's the wealth creation pipeline at work, a modern miracle that brought humanity out of the permanent dark ages and repeating Malthusian cycles.
For example, much of modern technology - silicon chips, mobile phone networks, etc, would not have been possible without a deeper understanding of quantum physics.
However, continuing this growth and wealth generation process depends on continuing to deepen our understanding of the fundamental building blocks of matter and energy. Stop or slow the latter and we stop or slow the former. To date, particle accelerators are key component of doing that. And even if someone discovers a better way, we'll still have to invest in that. Either way we still have to invest in the process of unveiling the deep structure of matter.