Despite strong incentives in the Republican tax plan for American executives to expand, invest, and ultimately boost the U.S. economy's growth potential, a lot of the debt companies are issuing appears to be motivated by something else.

Non-financial corporate debt stands at 45.6 percent of gross domestic product (GDP), near the highest level in post-war recordkeeping. Despite that, non-residential investment—a broad category in the national accounts that includes everything from office buildings to software—has only been bouncing around the 13 percent of GDP range since 2012.

“You would think that companies want to add to productivity capacity, but we really haven't seen it,'' says Priya Misra, head of global rates strategy at TD Securities USA. “If they view the economy as in the late stages of the expansion, then there isn't a lot of confidence about the outlook and it is easier to buy back stock.''