Well, that is the reason. Whether you chose to think it is a poor excuse or not, that is your prerogative.

And, as CIHY stated, an exceptionally high proportion of the pax originating in India transit on to Canada, the US and other destinations, of which the regular Vegetarian option in the cabin is not suitable, it was changed to ensure that they were able to be supplied with their meal choice throughout their journey, not just on the sector between LHR and their indian gateway city.

You try explaining to 30, 40, 50 pax on a HYD or an MAA that their is no hot meal for them because they/their travel agent has selected HNLM (which as you correctly state in the meal description in the OP is a non-veg option), yet they are expecting it to be a vegetarian. There is no way of resolving that situation in the air, non what so ever. So, I am very sorry that you are not going to get your SPML to your preference, but there are tens of thousands of customers every week who are delighted that they are getting food that they can eat on all of their journey, not just part of it.