Because he, like all footballers, will be doing that now anyway. Because that’s football economics. City haven’t got him to sign again with 3 years left and now we know that he has us over somewhat of a barrel.
Haaland signing next summer has fuck all to do with what Sterling demands right now. What Sterling demands right now will be determined by the market, ie his worth to City and the cost of replacing him less his sale value now/next summer.
If you think Sterling doesn’t demand his fuck whack now on the off chance City pay full price (and normal wage) for a top striker next summer then you need your bumps felt.