Chelsea sign 60 million pound a year shirt sponsorship deal with Nike
http://www.telegraph.co.uk/football/2016/05/17/che...
That's an awful lot of shirts to sell. There are not that many Chelsea fans in this world, especially if you take out all the new "life long since 2001" fans.
Chelsea and Man United are the only English clubs with any commercial value all the others are small fry.
GLOBAL SHIRT SALES
Team Shirts sold 2015/16
FC Barcelona 3,637,000
Bayern Munich 3,312,000
Chelsea 3,102,000
Manchester United 2,977,000
Real Madrid 2,866,000
PSG 2,212,000
Arsenal 2,055,000
Atletico Madrid 1,977,000
Juventus 1,678,000
AC Milan 1,287,000
http://www.dailymail.co.uk/sport/football/article-3588871/Chelsea-beat-Manchester-United-Premier-League-shirt-sales.html