why do people become seclusive when they go through divorces?

People need time to if you will, grieve over a divorce, and do not want people like you in their business. Leave them alone, they will come around in there own time.

People handle hurting differently. Some will seek out a lot of company to minimise their pain while others will choose to hide out to lick their wounds. Neither are wrong, its just because people aren't all the same and need to do things their way. 

Trust me, in most cases, they're the last you need around as many have assisted to your decline!

Inner work. Friends and family can’t fix that. 

That may be key to YOU, but some people 

prefer to handle their "difficult times" alone. 

There are few things I hate more than when 

people won't believe me when I've told them 

quite clearly that I needed to be alone for a 

while and they ignore that and pester me. 

Please respect their wishes. 

Not everybody deals with things the same way. Some people like being alone. 

I can only speak for myself.  My wife had a fiance'.  She made plans to marry another guy while she was married to me (we were not in the process of divorcing, or even talking about it).  My wife's fiance' broke up with her, because he caught MY WIFE cheating on HIM with several other guys.  Yeah, I know...that is a severely f*ck'd up situation.  I eventually got written proof that my wife was engaged to another guy and cheating on BOTH OF US.  I had proof that she was cheating on me, and she was also cheating on her fiance'.  Irrefutable proof.  In fact, the proof was so convincing that the judge in the resulting divorce case issued summary judgement in my favor.  He didn't even WANT to hear "her" side of the story.  Not only did she get NOTHING from the divorce, but she had to pay her own legal bills, also.  

HOWEVER....

When I filed for divorce, suddenly I was the bad guy.  Most of my so-called friends abandoned me as they thought I was being mean.  All of her family (most of which I was very friendly with) also turned against me, as they couldn't understand why I would be so cruel as to kick her cheating @ss out of my house.  I had other friends who I THOUGHT were loyal to me.  But I later learned that they were only pretending to be nice to me so that they could spy on me and try to dig up "dirt" for my wife to use against me in the divorce.

Basically, I had to leave my whole life behind.  I couldn't trust anybody.  Literally everybody I knew and loved, betrayed me.  Simply because I did what any self-respecting human being WOULD DO, under the circumstances.  

If I'm my only true friend, fine....I can live with that.  And as it turns out, I WAS  my only friend, at the time.  I have lots of new friends now.  But during divorce?  I shut out everybody, eventually.  They all betrayed me...  

Not having been divorced it seems one of the couples is better off after the divorce than the other and that leads to one being more subdued to enjoy life being single again.

They may be ashamed that they have let go of the person who meant so much to them a little while ago.  Family wished them all the very best, and they let them down.

They are also not sure if their friends have loyalty to the ex.