Because the survival of the tribe was of paramount concern, it was in the best interest of the tribe to see that it's children were married properly, hence the many laws regarding marriage and just how it affected the inheritance within the tribal structure. A wealthy landowner within a tribe contributed to the overall well being of the tribe as a whole and his assets needed to be protected from rival clans that would possibly use marriage, sex or the claims of a woman as grounds for taking away part or all of the physical property.

As far as everyone sharing the bride, that sounds more like a modern day fairytale of someone who has a social agenda they are trying to push.