Why TF do people do this to people they will marry in AM

I know a few people who are in a relationship for many years but are sure they wont be able to marry each other( Typical caste integration problem) but still would be together until their parents choose someone through AM.

I also know someone who has reached that stage and every now and then goes to hometown to see suitable grooms, and after coming back to city lives with her boyfriend in live in.

Consider me old school but i cant think myself pulling plug for one person and being for someone else the next.

One of the reasons for my breakup for over 3 years was her family had show resistance to intercaste for her elder sister (6+ years) and the madness that followed