There are many answers here, none particularly useful if you ask me. The easy on is one word: capitalism. Business is at the center of the economy - without any business motivations or funding from other sources such as the government, STEM isn’t lucrative in a capitalist society.
Even if most skills do get funding in some way, there are some that pose more challenges, such as that of the theoretical mathematicians: https://collegemathteaching.files.■■■■■■■■■■■■■/2013/02/appliedvspuremath.jpg
There are plenty of other valid answers here. I guess the real question is why you ask. What is this in relation to?
This is such a vague question. If you go to any “highest paid degrees” list, you will find a mix of business, computer science, engineering, and medical degrees at the top.
http://www.payscale.com/college-salary-report/majors-that-pay-you-back/bachelors
Many STEM careers are being outsourced to low-income countries. My corporation uses US-educated Engineering PhDs in New Delhi and Malaysia, paying them a couple of dollars an hour vs the $100/hr a US employee with similar educational background makes. BE CAREFUL when choosing your STEM major!