There are always lots of people wanting/considering moving between the fleets; equally, there are many valid reasons why people want to move fleet.
Some just want a change, others move to EF in order to get promoted/part-time (both these take much longer on WW), some don't want to come to work every day/want to commute from overseas (WW is better for this), some think the only 'proper' plane is a Jumbo...etc. etc. LOL, ok the last one was a joke...
Everyone has their reasons.
A good piece of advise is to put your name on every 'list' going...WW, EF, part-time etc. It's better to be in a position to turn down offers than to wish you'd put yourself on a transfer or part-time list.