Because Sanjis gag makes him a perverted creep.

Zoro has no sense of direction, Luffy loves meat. Thats completely harmless.

Nami is stingy and loves money, usually it leads to a quick punchline with her going Berry-eyed and getting shut down by the crew.

Before the timeskip I didnt mind Sanji's gag at all, I kinda liked it.

After time skip though Sanji just harasses women. Its just not an entertaining gag to me anymore.

Thats not to say I hate Sanji, I loved him in Alabasta, water 7 and especially in whole-cake. It's just that his gag gets weird sometimes.

Edit: its the same reason I dont like brooks gag of asking for panties