It's not just the shot that's criticized, the whole movement was way off.
There was no way the ball could reach Lukaku where he was running to, the path was blocked. The ball only reached Lukaku because it went in between the legs of the defender. The run was quite bad and showed lack of spatial awareness since the only way he could have received the ball where he was showing (can he stop doing this ffs?) was if his teammate dribbled past the other defender out wide and slotted an outwards pass to Lukaku. There also was no defender onto him so he could have ensure his run was better timed. He was completely unmarked. His defender abandoned him to go for the ball and Politano.
The execution was also quite bad because he opted for a first time shoot off balance when his body was facing the exterior of the goal. He had time to control it and finish it on the second time but he always prefers to shoot (or pass) first time no matter what. He's no 'killer' unfortunately otherwise that would have been 1-3.
You can also notice this with the last Politano chance. He's running in the correct lane per se, but he's completely ignoring that a defender was on his left and closer to the ball if a pass would take place, meaning that he wouldn't receive it for a tap in... Unless the pass was made in a very specific place, at a very specific time, assuming that neither ball marker and GK could reach it. Politano could have done better of course, but given how the situation was taking place, Lukaku's run was also off.