https://www.tandfonline.com/doi/pdf/10.1080/01402390.2016.1196357
It is important to recognize that jointness is not an unmitigated
good. It can, for instance, inhibit military innovation. Gholz and
Sopolsky’s study of the US defence industry argues that jointness has
led to the situation where the services have no ‘incentive to
experiment with new approaches.’17 Other studies support the notion
that inter-services rivalry is good for military innovation. 18
Another criticism against jointness is that unifying the services
creates problems for civilian control. Peter Feaver observed that a
more unified military maybe ‘better able to resist assertions of
civilian control.’19 As explained later, concerns about civilian
control have been at the heart of reluctance in India to appoint a
Chief of Defence Staff who would be the embodiment of joint planning,
training and operations,
It's the concerns about civilian control that explains India's reluctance to appoint a CDS.
What explains this reluctance to impose jointness? Civilian hesitation
towards appointing a CDS is due to a fear that this may weaken
civilian control and upset the supposedly ‘delicate’ civil-military
balance. This senti- ment has animated the Indian political class from
the 1960s – when the CDS was first proposed by Mountbatten – to this
day.
India believes that CDS would weaken civilian control over the military and upset the delicate balance between the civil part and the military part of the government.