I don't think it is puzzling. Technological advances have made each person capable of doing much more, and capital does more and more of the work that people used to (or someone in another country does it). I bet underemployment rate is not low, and with more and more people competing for low skill jobs where they're easily replaceable, again, thanks to technology, there is no reason for wages to go up.

Also of note is that more economic activity is concentrated in fewer and fewer regions, so while a select few (urban) regions experience growth and whatnot, most other areas do not.

There seems to be a trend among large employers to avoid full-time employment, either by keeping weekly hours below x or hiring contract workers.

We've seen since the last recession that top 2% have grown incomes while most others are stagnant, perhaps this is part of it.

I think the majority of technologic trends since at least 2000 have been fundamentally deflationary in nature, for all material goods. We simply are conserving more; using less materials and energy for the same set of consumer uses. Unlike the last industrial revolution where new energy hungry appliances were being invented and new ways of life expanding, most new inventions today are long lasting, low energy consuming, or are just innovations making existing products cheaper.

That central banks and treasuries insist on inflation above zero when we should probably be deflating and letting technology make everyone wealthier...no wonder there are property bubbles. (Note this inflation argument encompasses the effect of trade deficits in creating asset bubbles, because inflation/treasury debt breaks the trade/currency feedback loop)