LIMRA, which is supported by membership dues from insurance companies, also said inertia on the part of sponsors explains the lackluster uptake of annuities.

Two-thirds of surveyed sponsors said they recognize the importance of offering in-plan income options, but only one-third actually do.

"Employers remain unaware of the value inherent in these income options," said LIMRA's analysts. "Employers are clearly not convinced that their employees need or want these options."

That signals a disconnect from participants' interest in guaranteeing some portion of 401(k) assets into a guaranteed income stream: LIMRA says eight out of 10 participants are "very interested" in having income options as a part of their employer-sponsored plan.

The question of making guaranteed income products more accessible to plan participants has been raised in numerous contexts by regulators, politicians, and retirement security advocates.

Last summer, the Department of Labor issued a new field guidance to clarify existing safe harbors for immediate and deferred annuity options in 401(k) plans.

The new guidance addressed the "time of selection" clause in an annuity safe harbor created by DOL in 2008.

The original safe harbor said plan sponsors' fiduciary obligations in selecting an annuity provider are satisfied if appropriate consideration is made of "the information sufficient to assess the ability of the annuity provider to make all future payments under the contract."

Critics of that language said it exposed plan fiduciaries to liability if an annuity provider were to fail to meet its obligations to investors in the future, potentially discouraging sponsors from building annuity options into plan menus.

Last year's field guidance attempted to allay sponsors' fear. The DOL said a sponsor's assessment of an annuity provider's future viability is limited to the time of selecting the annuity, "and not based on facts that come to light only with the benefit of hindsight," according to the bulletin.

While the original safe harbor said periodic reviews of plan annuities and their providers are required, the new guidance clarified that sponsors do not have to engage in a new review every time a participant moves 401(k) money into an annuity. Sponsors are also not required to monitor a provider after their products have been removed from a lineup.

DOL's recently released fiduciary rule says advisors recommending variable annuities and fixed indexed annuities to plan sponsors will be beholden to the rule's Best Interest Contract Exemption. Because VAs and FIAs have variable compensation, advisors will have to use the exemption when recommending the products. Immediate annuities, however, do not fall under the BIC exemption's requirements.

Critics of the DOL rule say new restrictions on VA and FIAs may further discourage their adoption. Advisors have until January 1, 2018 to fully comply with new fiduciary rule