Answer:
Someone might choose an in-demand major to have a higher chance of not only getting a job but also having a high paying one. Choosing an in-demand major depends on what you care about in a job. If you only care about making a lot of money then it's for you but if you want to have a certain kind of job for a certain reason, say a doctor to help people, then it can be tricky because a major for that job or purpose might not be in demand. You could end up having a super boring job or one that doesn't fulfill you're intended purpose in life. Your why depends on you.
Step-by-step explanation:
I left the second part of the question more open-ended because I don't know if you consider choosing an in-demand major a good choice or not but my answer should help at least a little.