I received a letter from irs asking for me to send my w2 in. Why do I need to send them in. My tax situation was simple and nothing different that prior years??

The best way to deal with IRS is to simply give them whatever documentation they want.  They can ask for your W-2 because they have a mismatch with their records, or they can ask for it as part of a random review.  It doesn't necessarily mean there's a problem.

The sooner you give it to them, the sooner they'll move forward and (hopefully) send your refund.