Ask HN: why is bookmark syncing so hard?

Like most of you probably are, I'm using more than one computer and keep an extensive collection of bookmarks - needless to say I would like them all to be in sync. now for a while I've tried xmarks, which worked fine until it began randomly deleting some of my bookmarks. I then switched to chromes builtin syncing methods, which until now worked splendid. and now it stopped working too and this is apparently a common issue, as mentioned by others:

http://code.google.com/p/chromium/issues/detail?id=114047

http://productforums.google.com/forum/#!topic/chrome/cbUJnyae32g

Is there any reason that I can't think of, why this should be so hard? If google can't get it right, who else might?