Oda wanted to portray the contrast between:
1- Whole Cake Island/Zou: Sanji said "I will solve my problem on my own" and didn't trust the SHs when he was taken by Capone and still resisted Luffy's help
2- In Wano: Trusting Robin enough to say "save me" despite the fact Robin might fall into a trap, a complete faith!
Again, in terms of drama, character development and growth, Sanji has grown a lot....
BUT BUT BUT Odaaaa! Please, have mercy on our soul you bastard! Give Sanji a break damn it from Plot Losses!
Even if it is great for his character growth to have this change, there are other ways to do it... other ways to deliver the faith/trust plot line than this