research process - Why do students go for a PhD even when chances of getting academic jobs on its completion are slim?

This is in reference to my question: How to do a PhD to equip myself for a job as assistant professor.

I was told in the answer of the above linked question that chances of landing a job as an assistant professor in Mathematics are quite slim. Very few people will actually get a permanent position in academia.

An article of 2014 shows only 0.5-3% of PhD graduates will actually get a job as an Assistant Professor.

But I have two questions:

1. 
   
   

   Why do so many people still apply for a PhD in some reputed institutes in India even knowing the harsh reality? I found there are 1500 applications for four PhD scholarship positions.

   
   
   
   
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     One answer says that people move to industry, but I still don’t understand how after doing a PhD in suppose differential geometry or algebraic geometry one can do a job in industry if he/she gets no position as an assistant professor.

     
     
   
   
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     Will one be satisfied to do some managerial work in some Consultancy firm after doing a PhD in Mathematics?

     
     
   
   
   
   



2. 
   

   Are people jobless after a PhD? Completion of a PhD requires so much effort. So why is there no value after doing it?

   
   

NOTE:

In the most up-voted answer below it has been said that many who enroll for a PhD don't even wish to pursue an academic career.

I have been asking my seniors who are currently pursuing a PhD or are in the verge of completing their degree or who have completed it. They said that they all want to be Professors in some Universities and want to be involved in research because that is the dream job for them.

I am obviously talking about PhD in Mathematics

Answer

Some of my observations:

1. They don't know what they're going into. Most PhD students have some idea of how hard it is to get a job afterwards, but don't actually know. It's similar to how one can imagine what skydiving is like, but don't actually know until after trying it.


2. They're confident they can succeed. PhD students are some of the smartest of their generation. They were top of their high school class, top of their undergraduate class, they've never met an obstacle they can't overcome. Why can't they also top their graduate class, top the postdoc chain, and top the applicants for tenured positions?


3. The process worked for their supervisors, which makes them think it'll also work for the students. The supervisors are probably the people most influential in convincing undergraduates to do graduate studies. These are the people who've already did all of the things in #2. If they can do it, so can their students, and hence they encourage their students to try.


4. They don't know what they want to do. They haven't really thought about future careers and only have a vague idea of how their studies enable them to find a job if the academic path fails. The hidden reason they did undergraduate studies is because that's what everyone who did well in high school went on to do, and the same applied for graduate studies. "The best undergraduates do PhD studies, so I'll do it too".


5. They have romantic ideas about what people with PhDs do. When scientists talk about what they do, they don't usually say "I write funding proposals". The not-exactly-accurate answers propagate and influence the next generation of students to try to become scientists themselves.