Thing is you need a manufacturer that can manage and launch hybrid boxes (DVB-S2, IPTV, OTT), as well as chipsets with all the security needed (CAS).
And Broadcom are currently the best, and Technicolor exclusively launches with Broadcom.
S905X3 is good for OTT only STB.
Non availability of manufacturer is definitely NOT a limitation. In India itself there are some service providers offering higher end hardware ( S905X chipset and other quad core) with hybrid settop boxes. Dish , Hathway launched there set top boxes with S905x. Other operators in world also launched with higher S905x2 / S905X3 based Hybrid Set top boxes. There are vendors who customize and provide turnkey solutions for operators.
Also , S905X3 was just an example. Broadcom also manufacturers and is a market leader in providing higher end chip sets for hybrid Set top boxes. The problem is not about manufacturer or availability of chipset, it is about mindset of service provider (in this case Airtel).