> Hindi and Urdu, by any reasonable linguistic definition are not separate languages.
That is a common misconception. You are confusing colloquial Hindi and colloquial Urdu with the pure Hindi and pure Urdu.
Pick a word, any word and there is Hindi equivalent and there is a Urdu equivalent. Just because the spoken Hindi, primarily in India, uses a mixture doesn't make them same or even similar.
For linguists, the colloquial language is the most important aspect of a language, and it's actually very reasonable for that.
First, most languages do not have a written form, and for those that do, most could not communicate in writing until very recently.
Second, until very recently, most people could not communicate in anything but their colloquial form, and even then, most communication is colloquial form.
Finally, linguists are primarily concerned with analyzing what makes a language a language (vs. not a language) rather than what makes a language a language (vs. another language). For this reason it makes sense to consider only the colloquial language, since everyone who participates in a language to communicate and not for ideological reasons participates in the colloquial language, but the same cannot be said for "standard language".
That is a common misconception. You are confusing colloquial Hindi and colloquial Urdu with the pure Hindi and pure Urdu.
Pick a word, any word and there is Hindi equivalent and there is a Urdu equivalent. Just because the spoken Hindi, primarily in India, uses a mixture doesn't make them same or even similar.