British spouse but born and bought up in India partner visa Refused overstayer

Hi All my application for partner visa was refused.
We are legally married(6years) in UK and been living together for 9 years at the date of application.
We both are in UK more 14 years and 15 years (my partner and myself respectively)
My partner is british citizen and earns more than requirement threshold, but she is also born and bought up India. I am an overstayer since 2010. We both are now late 30s and came to UK in our early 20s
Application was refused saying we do not have any kids and if we wish to start family we can do it in India as we both are from there.
What I do not understand is In partner route law nowhere it says we will check where ur partner was born.
Current status of my partner is british citizen then why there is discrimination based on where is born.
please help and advice as we have to do appeal in 14 days

It is not discrimination based on where she is born. The same would have been the case even of a British citizen born and raised in the UK.

British citizens do not have a right to bring their family to the UK. If they want to live with their family, there is an underlying presumption that they can do so abroad/in the land of their partner. The idea that she can have her family in India is not because she was born there, but because that is your nationality/the nationality of her non-British partner.

Also see this thread of a British citizen trying to sponsor their wife from Turkey, in particular this post.

If you don't meet the requirements for a spousal visa (because your British spouse does not meet the financial requirements, for instance), then the application must be assessed to see if there are "insurmountable obstacles" to your British spouse and you living abroad (such as in the country of your nationality). If your British spouse was born in and lived the first twenty years of her life in the country of your nationality, the odds of there being "insurmountable obstacles" of her and you being able to live there appear to be negligable to non-existent.

But that only applies if you did not meet the requirements for a spousal visa. If your wife meets the financial requirements, what does the letter state as the grounds for refusal?