The thing about the multis that take a long time is that you have a restricted audience.
If I'm visiting Adelaide for a few days hoiday, I can't do something that takes a lot of different visits and time to do. In fact, I did try a multi in Bendigo when we were there for a week with disappointing results. We worked all week on it and on the last day we figured we had all the info needed but despite a fair amount of time, we failed to find it. Now if this had been at home, I could have gone back over it all, phoned a friend and gone back for a few more tries but of course, we couldn't. So in the end, it was all a bit sad
So if you can't follow through on the longer and more difficult ones, it's a bit disheartening to attempt them.
Similarly, if I decide to go to an area of Sydney for a day's caching and there are multis there that will take more than one visit, or may be rather difficult so you expect it to need a few visits, I'm unlikely to get back there again to finish it off. An hour's drive there and another hour back is just not generally worth doing twice or more just for one cache. I do have a few of these hanging around unfound and i suspect I will never finish them - by the time I go back, I've lost the paperwork.
So the people who are likely to do a multi that takes several visits will be likely to be only those who live relatively close. In this way, you kind of automatically cut the audience back to the numbers that were around back in the ealy days - which may be a nice thing sometimes I reckon
On the other hand, there are some caches that take a whole day to do which I will plan a special trip for just becasue they involve a great bushwalk. But the bushwalk may be the real drawcard becasue if I log a DNF, I need to feel it was still a great day's outing.
Don't be too hard on cachers who don't have the time to travel long distances to do long or difficlut multis