Just googling some trends I see the real drop started about
the same time as the economic collapse. Further the
long term decline also parallels with the mfr sector leaving the US over time. Which would likely mean a good portion of small business startups were in some manner related to a supply chain of support for larger mfr companies that left for other shores. Then you can go with the flat income for the middle class and them having less income to get something off the ground as they had to use more of what was their discretionary funds for supplementing living in general instead of investing it into a business.
...and Lucy it appears the issue isn't about regulation but in a small way. Frankly on the environment plus my being a parent and grandfather I'll error on the side of longevity instead of "I got mine, let them get theirs" mentality you display here. Not like Mars will be an option in the near future if we ruin this rock.