Terrible experience at London Heathrow Airport

I came back last Saturday from India and was asked just the basic questions that's it.
I usually travel due to business or holiday. I have had problem only for the first time (i.e. when I switched to T1 Ent visa) in which they grilled me. But after that every time the immigration officer would only ask the basic questions that's it.

I guess they are stopping people on the basis of their previous immigration history or if there are any red flags.