It just stems from the Baptists being historically independent, with each congregation being responsible for itself before God. Many formerly Baptist churches are now even removing Baptist from names and just becoming independent evangelical congregations. Though in reality the Baptist are no different that any of the other independent congregations with more & more variations of doctrine as people become satisfied by the opinions of men.
Baptists become the butt of jokes as a result of regional & political bias after the War Between the States because Baptist was the historical dominant denomination of the South. No different that the bias of describing all Southerners as brain-dead, gapped-toothed, inbred, uncouth fools.
That said I understand what you are saying. I was raised in southern Baptists churches, but I no longer attend a Baptist Church. I don't attend because I changed, I haven't. What was once my home church was turned from a solid, very effective, Bible preaching church into a Six-Flags over Jesus.