Even if you count June, there is only 13 weekends that are really available for a National Meet. Before or after that the weather just gets too unpredictable for most of the northern states. Take away four weekends for AVR, V2V and Sturgis (2), and you are down to nine. There are likely to be six regional meets during that time (SE in May and SW in Feb) which takes it down to three potentially open weekends. Now add in things like Meet in the Middle, Lil Sturgis, Laconia, etc, etc, etc. This doesn't even include all the local benefit rides that go on each year, or even local chapter rides. The truth of the matter is you just can't make it to every single meet or ride that is scheduled. Can't physically be done. You have to plan what to do and where you want to go. If the National happens to be too far away or conflict with something else you just have to say oh well, maybe next time.
Saying it should be on the same date could eliminate the possibility of ever making a National for some because of work commitments or family. (Have you ever coached baseball?)
Saying it should be in the same place would put a huge burden on a limited number of people year after year. You can do a lot by phone and via the internet but feet on the ground at the venue area is pretty much a must. Nothing beats face to face with the people you are working with and depending on to make the event a success.