Adoption of wearable technology is coming along albeit not quite at the pace that some companies may have predicted. Market research firm eMarketer said on Wednesday that it expects nearly 40 million adults in the US will use a wearable this year, which it defines as those who wear accessories or clothing that connects to the Internet or lean on another connected device with the purpose of exchanging data.

The firm expects to see double-digit growth in the wearables market over the next several years; adoption shot up 57.7 percent this year alone. That's not an outrageous or reaching forecast considering just 16 percent of adults in the US currently own a wearable.

eMarketer confirms a stance that I've had for years: wearables don't yet offer a clear or big enough value to motivate people to spend money on them. In other words, they don't really serve a purpose or fill a need. The firm also highlighted the high cost of some devices as another challenge that manufacturers face.

Low adoption rates also mean that advertisers haven't yet embraced the technology. Cathy Boyle, a senior analyst with the firm, said the consensus among experts they consulted was that advertising will not appear in volume on wearables until one or more of the devices attains significant market share.

App development played a huge role in the early growth of mobile devices and could potentially have the same impact on wearables. Above all else, however, they still need to serve a purpose and that hasn't yet happened in the eyes of many consumers.