In a clean text, I would write like this with your own words:

Not enough students choose science subjects at the university in a lot of countries. 

Now a lot of students choose subject from their own interest, so only a few study science subjects. I think this is a common phenomenon at universities in a lot of countries.

In my opinion, studing is for finding work in the future, so on their own ideal, they want to find joy on their jobs. A lot of students don't like science jobs, they prefer the other subjects, like dancing, drawing, marketing and so on. They want to work on these jobs in the future.

The science sujects is boring, so learning becomes very tiring and it must take a long time to learn such subjects in average, students have not many freetime to do other things.

It's impossible that every worker do the same job in the world, more and more people will choose their own future by studying some other subjects at universities.

In the future, less and less students will choose science subjects, but a lot will choose enjoy their own subjects of interest.

Topic： Not enough students choose science subjects in universities in many countries.

Nowadays many students choose to study subjects that they are interested in ,resulting in fewer students studying science subjects. I think it is a common phenomenon in university occuring in many countries. 

My opinion is that the reason why students study is to find work in the future. Everyone has their own ideals,and  wants to find enjoyment in their work. Many students don't like jobs in science, they like  other subjects: like dancing, drawing, marketing and so on, they want to find work in these areas in the future .

The science subjects  are boring, so learning the subject can be very tiring,and it takes a long time to study. Students have no free-time  to do other things.
It's impossible that evey worker does the same type of work in the world. More and more people will choose their own future ,studying different subjects in class.
In the future,less and less students will choose to study science subjects. However, many will choose subjects which they enjoy. 

* You don't have to put more and more- there is nothing wrong with it, but it seems a bit repetitive. 

More and more= More. Or you can say 'Increasingly' Less and Less= Less, smaller amounts, decreasingly ect.

* Have a look at any corrections I have made and if you have any questions, feel free to ask. I am British. I am learning Chinese at the moment hopefully you will be able to help me too!