Because it has India as a neighbour which will protect it in case of invasion from the Chinese. India helped in the formation of Bangladesh when it was struggling for Independence from Pakistan. We fought a War with Pakistan for its liberation.
We helped Bhutan too during the Doklam crisis. India won't and will never invade. So these small countries feel safe. The only time India failed was when India couldn't stop the invasion of Tibet by China. Subsequently, we also lost a War with China when it occupied a portion of Ladakh (Aksai Chin). That loss made us realise the importance of being a nuclear power. So India strengthened only when we acquired nuclear capabilities. That has kept both Pakistan and China in check and ensured some form of stability for the smaller countries that share borders with India.
We helped Bhutan too during the Doklam crisis. India won't and will never invade. So these small countries feel safe. The only time India failed was when India couldn't stop the invasion of Tibet by China. Subsequently, we also lost a War with China when it occupied a portion of Ladakh (Aksai Chin). That loss made us realise the importance of being a nuclear power. So India strengthened only when we acquired nuclear capabilities. That has kept both Pakistan and China in check and ensured some form of stability for the smaller countries that share borders with India.