They tend to be categories in which the products are essentially frivolous commodities - cigarettes, alcohol, fashion to name a few.
These products are essentially identical and are bought primarily for the image or inferred status they give the buyer.
However, because these products tend to be heavily advertised in a certain way, some public transport marketers think the rules that apply in these categories apply in theirs. They don't.
Most products are bought for specific, concrete reasons -- they taste better, work better, look nicer, are more convenient, or cost less. The emotional buttons that work to motivate sales of perfume simply don't work when you're selling something that takes you to Asda on a Tuesday afternoon for £2.50.
And yet we constantly hear marketers talk about the need to make "an emotional connection" with consumers. Agreed, it never hurts if people have positive feelings toward your product or brand but in most categories it takes more than that to motivate a change in behavior.
Surely it would be far more productive to make a logical connection -- a good solid reason to try your product -- than an emotional one? Just a thought.