Some supposed Singh's out there will say it's to symbolize that the husband is the leader and the wife is to obey and be his follower in the marriage. However they don't get the metaphor and they are so wrong because that goes against what Gurbani says about equality.
The metaphor is that in Gurbani Akal Purakh is portrayed as husband lord.. the only male while all humans are considered soul brides or female. Of course it doesn't literally mean Waheguru has a gender or that males are closer to Waheguru because their gender is used as the symbolism for God. Why human marriage is even used at all as the metaphor is because it's the ONLY relationship as a human that we can understand that is in any way close to experiencing the merging with another soul. (One soul in two bodies).
Now, culturally it was the girl who left her parents home to go to her husbands home. (she would symbolically follow her husband to a new life). This is not to say that cultural practice is or was the ideal or what should be or has to happen, but it was the common norm - so it was used as the comparison that most people would understand the metaphor!
So the metaphor during the lavaans has nothing really to do with the human marriage but instead of our souls male and female both (soul bride) following our husband lord (Akal Purakh) and becoming ONE (symbolized by the Palla connecting them together). To accomplish this as a married couple, we put SGGSJ at the centre of our lives together as a married couple (hence the circumambumations). Basically a married couple make a commitment to Waheguru Ji that they will lead spiritual life together and keep SGGSJ at the centre of their lives together with ONE shared goal.
In NO WAY does this mean a husband is to be seen as some God over his wife as many like to think!!!!!!! (And some deras / sampradas actually teach this untruth!) The symbolism is like a play. In marriage both partners are equal and make decisions together. The wife isn't some subordinate made to obey her husbands every whim or destined to only serve him and never be served. It's just to put a subconscious idea in the mind that our soul trying to merge with Akal Purakh is akin to a marriage where two souls become one and to do that a cultural idea was used to convey the message - that being that culturally the girl left her parents home following her husband to embark on the journey to merge with her husband's family in a new life together. It doesn't mean that the Gurus agreed with this cultural norm of the time, and we can see plenty of metaphors used in Gurbani where an older idea was used from Hindu mythology etc to illustrate an idea - but it does not mean that the Gurus agrees with that older Hindu idea at all!!!
In reality the husband and wife are both in the position of the bride (soul bride) in the lavaans, and as absolute equals together when it comes to the real journey together toward Waheguru...
Does that make sense??