Monarch caterpillars: creating the best environment

This is the first year I planted asclepias tuberosa. I didn't get any flowers but I was shocked when I noticed a ton of monarch caterpillars. I watched them grow daily but also watched with anxiety as my milkweed leaves depleted. I was concerned that they didn't have enough food to make it to pupal stage but then one day they were all gone.

I learned that they leave the milkweed to form their Chrysalis, looking for a high and safe place. I've looked everywhere but see no sign of their chrysalises.

A couple weeks later I noticed a new batch of tiny monarch caterpillars. But after a couple days the biggest one seems to have died from a bacterial disease.

Without blooming my asclepias tuberosa enticed monarchs to lay their eggs. Even though I see tons of blooming batches of the tuberosa around town, I haven't seen any caterpillars on them or even signs of caterpillars having eaten the leaves.

I also planted asclepias syriaca in the same location but no eggs or caterpillars have been on that plant on their own. I did move a few of the cats to it once it was clear they were going to all finish the tuberosa before they were ready to change and needed more food. They did chow down on the syriaca once placed there.

Things I've learned from this experience and things I may do differently next year. Also some questions for anyone with more experience than me.

1. milkweed flowers seem unnecessary to entice monarch butterflies! As long as the milkweed is next to a pollinator friendly flower. My lobelia cardinalis is in full bloom and right next to the milkweed. I assume that's what attracted the monarchs. Don't know why they choose the tuberosa over the syriaca though. Flower variety and ensuring there's always something in bloom is definitely the way to go.

2. place your milkweed in a part of your garden that allows for the cats to safely travel to a high place to form their Chrysalis. This may be a problem with my placement. I don't know if the first batch of cats made it to a safe place. My milkweed is right up against my fence leading to my neighbor's yard.

Also, the milkweed I've noticed people planted in the middle of parking strips, where there's no trees or deeper woods for the cats to travel to, may be setting them up for failure. Never would have known this before!

3. any thoughts as to what killed the one that seems to have melted into black goo?

4. any thoughts as to why they seem to prefer the tuberosa over the syriaca?

I hope my first batch of cats made it somewhere safe to change. And I'll be making some adjustments in the future.