The roads and facilities in and around Yellowstone are opening later than normal this year. The official reason is budget cuts. Further discussion of the reasons would probably not be appropriate on these forums, but I'd be happy to express my opinions offline in private messages. I also hear that full opening of Yosemite and other mountain parks may also be delayed.
Disclaimer - if you choose to discuss this with me in private, my opinions are mine alone and are not sanctioned by the management.