Lilacs keep dying
It did not take too long to see the problem. It appears you have extremely sandy soil. You may even be on the shoreline of a lake or Saginaw Bay. Most plants cannot survive in sand alone. They need a soil that has other components so that the soil can hold onto water and nutrients. Water and nutrients pass through sand extremely quickly.
Your two choices are: Grow plants that like very sandy soils (we do have many native Michigan species that grow in sand), or (2) supplement your soil with compost so it can hold more water and nutrients by the roots of the plants. The latter may be very difficult because even the compost, too, will eventually break down and drain through the sand particles, and you will have to replace it every year. My suggestion would be to either grow the plants you love in containers (or raised beds with newspaper at the bottom to slow the drainage but still provide some drainage), or opt for those sand loving plants I mention.
Here is a nice resource for native sand loving plants in Michigan:
Many "xeric" type plants can grow fine in sand soils too. Try searching for "xeric plants that grow in Michigan" to see the choices in that category.
To find some of these plants, contact a locally owned nursery to see if they can order the plant for you. You can also search "native plant nurseries in Michigan" to locate a handful of places that carry or order native plants for folks.