Because this is what Prem Chopra does. Grabs the girl forcefully and tries to molest her. Prem Chopra’s Prem is a bad guy. He is lecherous, he molests and rapes women.
Whereas the Prem whom Salman Khan plays repeatedly is an icon of mush. Since Maine Pyar Kiya (1989), Salman Khan has played the character 15 times. Prem is best remembered for the Sooraj Barjatya films. In his new film, Prem Ratan Dhan Payo, Salman reprises the role of the virginal-slash-saintly hero who embodies the Indian romantic lover. Whether there is such a thing at all is another matter.
The bratty Prem of Maine Pyar Kiya falls for a "sanskaari" girl whose on-screen father Alok Nath went on to become a very popular meme many years later. The Prem of Hum Aapke Hai Koun..! (1994) sacrifices his love for his elder brother. The Prem of Hum Saath Saath Hain (1999) is shier than his bride-to-be.
This Prem’s success with the masses may have to do with the aspirations of those who want to be see themselves, or other men, in that romantic idol mould. But the name itself is not a guarantee to the box-office. For, every other time that Salman has played Prem – a crook, a womaniser, a buffoon – all that a romantic hero isn't, the film has not replicated the success of the Barjatya stock character.
There was a time when it was hard to imagine Amitabh Bachchan as anyone but Vijay – the do-gooder angry young man who wanted to change the system and set it right. The Vijay of Zanjeer (1973) was finely etched in the psyche of an audience despairing for a channel to voice their concerns in a rapidly changing socio-political climate of corruption, nepotism and low economic growth in the 1970s – and what a deep baritone it was!
Amitabh went on to play Vijay in 22 films, always angry and fighting with a halo of moral rectitude around him, which faded over the years as Hindi cinema moved from show-causing to shallow showbiz. Mainstream films were stuck in a rut in the 1980s even as Bachchan kept playing the same angst-ridden hero. Then Prem came along and ushered in a new wave of candy-floss cinema.
Of course, there was Shah Rukh Khan too. He has played Raj seven times and Rahul, six times – intense lovers all of them. Aamir Khan briefly played Raja thrice in the 1990s before diversifying into different characters. Ajay Devgn, whose real name is Vishal, has from his very first film, Phool Aur Kaante (1991) repeated his screen-name Ajay, whom he's played 11 times, the last being in U Me Aur Hum (2008), which he acted and directed.
Whether it is Barjatya's first film, Maine Pyar Kiya, or his most recent, Prem Ratan Dhan Payo, each and every Prem, including the ones in Main Prem Ki Deewani Hoon (2003), Vivaah (2006), or Ek Vivah Aisa Bhi (2008), is a cardboard cut-out of the Indian family guy, wholesome and holier-than-thou.
Unfortunately, in Hindi cinema it's either this Prem or Prem Chopra. There are no shades of grey.