Why Delay Concession?

 Because, as long as Trump delays, he can push through some actions that enhance the chances that that vaccine will be released ASAP (not when our New Overlords permit it). The minute he concedes, he gives the DS an excuse to slow-walk all orders.

• He can get the vaccine out - in the hands of those who will be needed to distribute it (military, national guard, police, health personnel). Once out, whoever is in charge can no longer use that excuse to imprison people and cripple out economy.
• He can continue de-classifying Deep State activities. Once the penalties for disclosing the are gone, the files will be fair game (and, should anyone want to do a 'data dump' into a flash drive, at least they won't be charged with a High Crime).
• He can appoint Special Prosecutors for the Biden crimes, the Coup, and other activities that would otherwise be buried. Direct that the Senate have access to that information, and be the oversight choice. Make it an explicit part of the order that no person that is a target for investigation, nor connected to them, can have access to the investigation, or be permitted to slow-walk delivery of documents. Direct that the information in that investigation be presented to Congress, by June, 2022, in full. (Probably will be fought, in and out of court, but - give it a try).
• Move as much of his assets (and those of his family) out of the reach of the US Government. Same with family members - get them out of the reach of a vindictive opposition. Lawyer up, and get his security team in place (I wouldn't trust the SS people THEY would assign me).
• Make a book deal - in Ireland (or any other country that doesn't tax the money). Perhaps work with Indian publishers, who have a worldwide reach, and a relatively friendly government.
• Set up the structure that would give his message access to Americans - probably a combination of Internet subscription/some free/cable deal/radio. Use the connections he's built to work from the local level up. Help purge the GOP of the RINO detritus that has clogged the apparatus.
• Set some "information bombs" to go off at selected intervals throughout the next few years.

But, the ability to get the vaccine out there, and the mechanism for delivery in process, BEFORE the Biden-Harris administration takes over and does their best to dismantle it, is the most critical. I'm betting on Trump for this - he is experienced at moving big projects through ON TIME.