US homebuilders haven’t been this happy since the dot-com era. Not even the housing mania of the mid-2000’s had builders feeling this good about things. According to the National Association of Homebuilders (NAHB), the trade group that represents firms in the industry, their sentiment index registered a blistering 74 in December 2017.

Predictably, that’s got a lot of people excited about everything from housing to general economic prospects. Confidence is a big part of mainstream economics, and for good reason.

Developers, though, aren’t even sure why they are so enthusiastic right now. According to the NAHB, they were dead against the Republican tax reform plan working through Congress but apparently have flipped so as to use it as an excuse to be nakedly optimistic.

Homebuilders had been vehemently opposed to the Republican tax plan, which is set for a final vote in Congress this week. Changes to both the mortgage interest deduction and property tax deductions were seen as removing some of the benefits of homeownership. Apparently, builders now see the business incentives in the plan as outweighing those other negatives.

There are, of course, other possibilities. It may just be that like consumer confidence, or manufacturing sentiment, emotions no longer correlate so strongly with actual, realized activity.

The NAHB’s survey of member firms isn’t exactly a robust gathering of data. Splicing together series drawn from three different parts of the single-family segment, it asks participants to break down their views into essentially three buckets (Good, Fair and Poor in the first two, with the last rated on a scale of High/Very High, Average, and Low/Very Low).

Homebuilders feel like its 1999 but are building at a pace more like 1992. That’s a world of difference without accounting for the changes brought on by time. Actually, its worse than that, adjusting for population growth the single-family stock of homes is way, way behind no matter that it’s been growing for years.