People on here keep saying that it is done to avoid level busts, or that its better than them getting it wrong. Saying confirm at the end of each readback won't stop either from happening. The ATCOs silence is their confirmation that they got it right, and they need to be taught that. It is my job as an ATCO to listen to their readback. It is my job to correct any errors they have made in their readback.
For that reason I ignore the confirm at the end of the readback if the readback is correct and I find 90% of the pilots don't push the issue and if they do I tell them that by me not correcting them, confirms to them that they were correct in their readback. I know trying to change this part of the world one pilot at a time is probably a waste of time but you gotta at least try.
P.S I posted a thread on the Indian pilot forum on here and they all said they do it for a multitude of reasons, the main reason being a lack of confidence in themselves, whether due to language or culture.