It may be because of the difficulties involved in finding a convenient meeting time for group members who live in several different time zones. It may be because most Internet collaborators are volunteers who work on the collaborative project on their own time, or at work when their bosses aren't looking. It may be because it is so easy to communicate over the Internet without a meeting that we often forget the value of meetings. But I believe periodic meetings can be valuable, even if they are virtual. In the Internet groups I have been involved with, rarely do I get a sense that anything has been resolved.
Discussions drag out over days, weeks, or months.
If a decision has to be made, a vote is taken or someone makes an executive decision, but rarely do group members consider the decision to have long term consequences. The next time the issue is raised it is likely to be debated again as if it hadn't been previously discussed. Part of the problem with not having meetings is that decision-making becomes a bursty, asynchronous process. Often someone will introduce an idea for consideration and then promptly leave town for a long weekend. By the time they get back their proposal has been misinterpreted in five different ways and a discussion is ensuing about an issue that the initiator never intended to propose.