Tony's right...
If we're going to chart trends on these things, we have to stick to one set of units.
Self-employment is one factor, but the first chart on the series I linked to shows self-employment as counting for less than a quarter of the discrepancy. The rest can't all be new businesses, can it?
The second chart on that page shows the greatly widening discrepancy. I would give a lot to see that chart extended back a few more years to see if this has happened before.