some people looking for PR in order to monetize their blogs/site. that's what PR meant to them. some are just going for higher PR for the fame...some doesn't really care for PR or have any clue on PR at all....
Your pr depends on the number of higher pr backlinks, not the number of backlinks. If you have links from pr5 or higher even if only from 1 site you will get a pr3 or higher.
More backlinks is one of the factors to increase the pagerank.There are many factors to increase the pagerank.It depends upon the site domain age,the site content and quality etc.