I don't completely agree with you because the performance of Lukaku is this season is not good enough to say he worth trying hard and paying a huge amount of money for him, Lukaku was injured in many games and he couldn't help his team for weeks, however after getting recovered Lukaku could show in the last week but all we saw from Lukaku was just in a few last weeks which is not enough to say he had a good performance.
After all this, if the team still finds him worthy of signing then they can see some potentials in him that’ll help their team grow to new heights. If the amount Chelsea is asking for is very big and the player is not worth it, they could have backed out of the deal but they keep pushing and hope that Chelsea will reduce the said amount to a lesser one. This is football and there’s business in football. In as much as you want a player very desperately, you’ll be ready to pay extra fees than what he’s worth in order to have him by your side, I think that’s just the case here between Inter Milan and Chelsea about Lukaku.