I believe one of the main reasons is that IRS regulations for e-file providers require maintaining tax records separate from other record for at least 7 years. I do not see how it would be possible to merge accounts and be in compliance with IRS rules.
Also, even if the same ID and PW there is no guarantee that both accounts have information for the same person. It again would be a violation of IRS rules to mix tax information for two different persons.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
