NYC of the 70s-90s was considerably different from today: much less safe, bankrupt, gritty, dirty...while you might have seen and smelled some trash, it's not at all like it used to be.
The areas of Manhattan you'd be likely to visit are very dense and there are generally no back alleys so, even with the system working as intended, there can be a lot of trash that ends up on the sidewalk waiting to be collected. Yes, in the summer especially, Manhattan gets hot and smelly. There's a reason that a "house in the Hamptons" is something of a meme for wealthy New Yorkers.
When I lived in Manhattan one summer, during a time when the city was "rougher around the edges" than today, I was definitely ready to get out of town on a number of weekends.
> there can be a lot of trash that ends up on the sidewalk waiting to be collected.
Correct my if I'm wrong, but they still put bags of trash out don't they? Those things also attract rats who can easily chew through the bags or they can not be tied up properly in the first place, allowing he smell to escape. Why don't they use tidier, less smelly wheelie bins: https://duckduckgo.com/?t=chakra&q=wheelie+bins&iax=images&i...
http://all-that-is-interesting.com/1980s-new-york