Parliament has shown itself incapable of reaching agreement so a few extra weeks won't have any impact
Parliament aren't there to just decide on brexit.
They are our legislative body. They pass our laws. They are there to hold the government to account. Preventing parliament doing either is illegal.
Proroguation takes four to six days normally, the government were unable to explain to the court why they wished five full weeks. In such a turbulent time as eight weeks before brexit and their role was key.
As such the court has deemed the very unusual five weeks, with no explanation at all as to why it was required to be so long, served no purpose other than to prevent parliament doing its legal duty.
Governments have to abide by the laws of the land. There is no ways round it.
He decided to do it to prevent parliament carrying out its duty with no reasonable justification provided. He then subsequently lied to the queen about why he wished to do it, and to gain royal assent.
He also may be held on contempt of court on his return, on two counts, as he has refused to hand over the full documents for proroguation and yellow hammer as he was required to do.