Not really. As noted in the article, Thomas Cook merged with MyTravel Group in 2007, which almost collapsed in 2011 and left them with a lot of debt. Brexit cam

Not really. As noted in the article, Thomas Cook merged with MyTravel Group in 2007, which almost collapsed in 2011 and left them with a lot of debt. Brexit came years later. Possible causes would be long term trends in the types of holidays people want, increased competition, mismanagement, etc. But the problems started long before Brexit.