I sent a mail to the IRS in Sacramento on 2-21-29 and as of today, it shows that it is still in Sacramento and not reached its destination. Can you tell me why the delay?

Maybe because 2-21-29 is in the future.

I had similar worries when I sent return receipt mail a few years back & didn't get confirmation of delivery after a about 2 weeks. This is what I found was the reason for the 'delay'. IRS in Modesto has it's own zip code for the city block it's located on. All mail is delivered there but the return receipt isn't sent until one of the employees physically picks up the piece of mail to open & deal with it. As they get hundreds (thousands) of pieces of mail this can take some days. May or may not be the reason in your case, but it's a possibility.