Backup strikers at top clubs these days have to be one – if not a combination of – the following:
Relatively unambitious (Remy).
Too old to expect a first team spot (Drogba) or too young and unestablished (Wilson) to expect a first team spot.
In decline or poor form and thus understanding that they do not merit a first team place (Falcao, Soldado, Van Persie).
Willing and able to play another position in order to get game time (Walcott, Welbeck).