Why are some jobs tip worthy?

I agree, we have been socialized to find it acceptable to tip for some jobs/ services and not others. Having sold women's shoes in high school, waited tables and bartended, I can say that, for the most part bartending was the easiest for me. Dealing with what we called "Pretty Woman Syndrome" where ladies would come in, try on five pairs of shoes and then walk out is far more taxing than making an old fashioned or a martini.

Some jobs simply pay less, even though the service provided is more intensive.

I agree. I think the world has gotten too greedy. Most people are overworked and underpaid. Setting a tip jar out there is not the answer. It kind of looks pathetic to me. Plus most of the people doing are slackers. When I tip it's because I received great service, above and beyond what is expected. Not because someone put cream cheese on a bagel for me.

Your salary is your reward for doing your job. A tip is for extraordinary service.

actually i disagree about anyone getting a tip. Restaurants and bars and cab company's and all the others should have to pay wages just like any other establishment. I don't like having to be bothered giving tips.

well because they are jobs no one usually wants to do.

and it's the American thing where people in customer service expect to be rewarded for doing their job...

It's called "wishful thinking."