Jalandhar is surely famous but whether its more famous than other cities like Amritsar and Ludhiana is debatable.
Popularity of a city depends on a lot of factors like industries, education centers, historical significance, popularity in media, famous personalities etc. Following are some of the factors(not exhaustive list) which I think contribute to its popularity.
Entertainment Industry: It is the biggest reason for the city’s popularity. Sidhu’s famous one liner “Chuck de phatte napp the gilli, svere JALANDHAR shaami dilli” has a big role. Also a lot of Punjabi character in movies and tv shows are shown to hail from jalandhar.
History : It is one of the oldest city in India and oldest in Punjab (with earliest recorded mention of the city in 100AD!!!).
Religious Significance: It is named after a very powerful and popular demon according to Indian Mythology. It is also believed to be the birthplace of Tulsi plant (At Tulsi Mandir but its not that popular).
Location : The area has had one of the most fertile soil in India.
Industry : The city houses the largest(along with Meerut) sports good industry in India.
NRI Population : Jalandhar district(Doaba region) has the largest NRI population in India.
Media : It has Doordarshan Kendra and All India Radio were the only regional electronic media before the newer TV channels and radio stations in the Punjab region. It also serves at regional headquarters for many newspapers.
Hospitals : It has world class and highest number of hospitals in Asia.
Education : It has good regional colleges and universities like NIT, DAV, Khalsa college, PTU etc. Now it also houses LPU which has made its name for being the largest Indian university and a center for those who don’t get into other colleges (:P)
Famous Personalities : Yash Chopra, Jagjit Singh, IK Gujral, Harbhajan Singh, Sugandha Mishra(Recently she made Jal really famous in comedy world) and many more are from Jalandhar.
Jalandhar Cantonment: It is one of the oldest cantonment in India established in 1848 and has played a very important role in many wars.