Why is my tax return taking so long to be approved?

Has not been "accepted" or has not been "approved?"   Those are not the same thing.

“Accepted” is not the same as “approved”.  TurboTax tells you the e-file was accepted if the IRS deems that there is enough information on the return for them to take it in for processing.   Only the IRS can approve of the refund, which is a later stage of processing.  If the IRS approves your refund they will provide a date for the refund to be issued.

The IRS does not use the word "accepted" on the refund site.   

FROM THE IRS WHERE’S MY REFUND SITE:

https://www.irs.gov/wheres-my-refund

How it works

Where's My Refund shows your refund status:

• Return Received – We received your return and are processing it.
• Refund Approved – We approved your refund and are preparing to issue it by the date shown.
• Refund Sent – We sent the refund to your bank or to you in the mail. It may take 5 days for it to show in your bank account or several weeks for your check to arrive in the mail.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-refund/refunds-take-longer-others/L14YlqFrH_US_en_US?uid=lexdr7zh

.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-refund/irs-refund-taking-longer-21-days/L2vRAJbdU_US_en_US?uid=lexe7lst