Among other things, the decision that Chelsea will make is to sell Lukaku to another team and that will end their time together rather than Chelsea having to lose money when his contract expires.
They spent big transfer money for Lukaku and got limited contribution from him. They clearly know that they are counting down season by season till the contract expiration and if they continue to send Lukaku to other clubs as a loaned player, they will come to a contract expiration without any money from Lukaku transfer.
In addition, in loan transfer, the salary for Lukaku will be shared by Chelsea and the club which borrow Lukaku. Not all clubs will be ready to pay 100% salary for Lukaku and Chelsea surely are not happy to pay salary for a player who does not play any match for them in one season.
So far, Lukaku has been reluctant to return to Chelsea and he has asked Inter Milan to approach Chelsea to increase the option of extending the loan period for him. Even though Lukaku managed to lead Inter Milan into the Champions League final this season, if you look at the transfer market this season, of course he was very quiet from the European teams' targets for him. The only two teams that came to Chelsea were AC Milan and the Saudi Arabian league team.
It seems that there is really no strong desire for Inter Milan to make Lukaku a permanent Inter Milan player because they don't have enough finances to do so and one of Lukaku options is to join Ac Milan even though he will be labeled a traitor but that is one way for him to play in europe.
Inter Milan still needs Lukaku as an alternative striker but they know that he does not fit to be their main striker. The performance of Lukaku for Inter Milan in the past season is disappointed somewhat and it is much worse than seasons ago when he scored a lot of goals for them and won Scudetto with them.
The lack of interest from top clubs in Europe is understandable. So far Lukaku failed in Chelsea (two times), Manchester United and somewhat in Inter Milan too. It is difficult for big clubs to believe in Lukaku as he is getting older too.