Why can't a team surrender unanimously at any time?

If you really think about it, if a whole team wants to surrender, why should they not be able to end even before 15 minutes. This is coming from a guy who really doesn't like to surrender, but it doesn't make much sense for a team to be restricted from surrendering before 15, at least if the whole team wants to surrender. A team that unanimously wants to surrender should be able to do so at any time.

And for those who would just get annoyed by an early surrender vote, I guess there could be an option to always say no to surrender votes before 15 or 20.