But there are a few things going on.

1. Wednesday, the FED indicated growth will slow to 2% in 2020. Seems it's skeptical of the staying power of the tax cuts, deregulation, repatriation, etc.
2. Fear that rate hikes will choke off expanding economy (thus, the long end staying relatively anchored)
3. The globe was cooking earlier this year. You're starting to see cracks in Europe.
4. ~ $10T of sovereign debt still has negative interest rates, providing a bid for our debt.
5. Demand for long(er) dated debt remains strong, especially by insurance companies, sovereign wealth funds, and pension plans.
6. Flat(ter) curves typically signal late(r) innings of the economic cycle.

Throw all of that on top of inflation that still can't hit 2% (by the FED's preferred measure, the PCE deflator) and you have a yield curve (at least the part that the FED does not control) that is stuck.