Agree 100% with your view on the club's intentions. They want modern players who fans recognise, rather than pictures from 50+ years ago of players who only the most senior of fans will recall. It makes sense, and the club is quite entitled to do this, with or without fan participation.
Why, however, dress it up as something it is not? Why talk of "all time" legends when that is not what you want? Why deceive fans into thinking that they can vote their recent heroes into an all time team when, through the choice of Twitter, you are making sure that effectively they can't?
Marketing is by nature manipulative, but in this instance there is no need for such manipulation. We are fortunate to live at a time where the club is, in most instances, very transparent in their actions, yet on this occasion someone has come up with the idea of a skewed vote to achieve the club's aim. It's so unnecessary - just tell us what you want, and the fans will (largely) be happy to go along with it. Don't give the impression that you think you are cleverer than us. An own goal IMHO.