we go to a large family party hosted by one of two people on christmas eve. they take turns. the issue often comes up "who will do it in the future" referring only to those of us who have a house large enough to fit everyone. there are 8 aunts and uncles, who have been doing this forever, but honestly, none of the cousins want to host it, and the fear is if they do it once, they will forever be in the rotation. i myself like the relaxing of holidays and have no desire to plan, host, and clean up a party for 65+ people, all the night before christmas. i think this is especially true of those of us with little kids who have to make sure christmas morning is set up. imo, it would be easier if my kids were grown.
based on my own experience, i see nothing wrong with you just honestly telling everyone well in advance that you have hosted a wonderful tradition for over 20 years,but arent up to it anymore. you may pick one reason if you feel the need to give it, but i wouldnt necessarily go into everything to make someone feel bad.
but remember, you wanted to host the party, which was great, but it was your choice. its not up to you to make any else feel obligated or guilty to follow the same tradition. if someone offers up, great, but i think it would be very unfair to put others on the spot.
there is a chance that for the last 20 years, some have told other invites no, when they really wanted to go. there is a chance that some may be relieved to finally break this obligation. there is a chance that everyone may go their separate ways. just be prepared for that. i usually see families getting together with their immediate members only once the traditional party ends. but once your kids are married with kids, you can start your own traditions with them and their spouses, which will be much more managable.
there is also a completely different way to go about it, i know some people go away on a holiday to break the tradition. nothing crazy, just for 2 nights. then the next year, they proceed with different plans. all is takes is one year of something different.
good luck. the holidays for me cause a lot of stress in my marriage, and im already cringing at the thought!!!
ETA-just wanted to add, this is my inlaws, so maybe i would feel different if this was a party i had been going to since childhood. the majorty of adult relatives are male which does make a difference. (cousins 3 woman,14 men and 2 aunts, 6 uncles), so most of the women are by marriage and are only here a few years to see the tradition. i also think if it werent christmas eve, more people would be willing to host!