The Bingleys return to London for some time after acquiring Netherfield Park, as a result of Darcy working behind the scenes to keep Mr.Bingley and Jane apart. London is much more metropolitan than Hertfordshire, and is seen as a higher status place to have a residency. Jane eventually follows and stays with family. 

“ ‘When my brother left us yesterday, he imagined that the business which took him to London might be concluded in three or four days; but as we are certain it cannot be so, and at the same time convinced that when Charles gets to town he will be in no hurry to leave it again, we have determined on following him thither, that he may not be obliged to spend his vacant hours in a comfortless hotel. Many of my acquaintance are already there for the winter: I wish I could hear that you, my dearest friend, had any intention of making one in the crowd, but of that I despair. I sincerely hope your Christmas in Hertfordshire may abound in the gaieties which that season generally brings; and that your beaux will be so numerous as to prevent your feeling the loss of the three of whom we shall deprive you.’
'It is evident by this,' added Jane, 'that he comes back no more this winter.'
'It is only evident that Miss Bingley does not mean he should.'"

"Jane had already written a few lines to her sister, to announce their safe arrival in London; and when she wrote again, Elizabeth hoped it would be in her power to say something of the Bingleys."