Bhai Insat 4A and GSat 10 are not having Vertical and Horizontal Transponders respectively. As you know Insat 4A is already working in grace period & due to retire very shortly, infact in 2014 Tata Sky faced a major blackout due to power issue on Insat 4A (you can search it on Google) hence it lead to major fight with ISRO over delay in providing additional or back up satellite. They didn't have any option back then to get more space nor were in a position to migrate to new orbit as it would have led to crores of expenditure + logistical nightmare & after spending heavy amount in MPEG4 migration as emergency step they continued using Insat 4A , later they got 12 additional transponders from GSat 10 thus acting somewhat as a lottery for them.
Though they have been using transponders from Insat 4A but since then tried to gradually reduce load on it , changing home tp from 11010 H to 11050 H was mainly bcoz former can't take more burden. GSat 10 is a new satellite and they can easily activate Horizontal frequencies on it by using "Frequency reuse" option till they get new transponders next year & ditch Insat 4A right now itself. Please remember that it will be a temporary measure as implenting it reduces life of satellite. Most probably in December Tata Sky's contract for Insat 4A will end and instead of paying additional money for extending it by few months, they will likely opt for above strategy.