Are Sikhs Hindus because Sikhs intermarry with Hindus?

If you consider Sikhs as Hindus because they intermarry, then do you consider Jews, Christians, Buddhists, etc., not up to their respective religions as they too intermarry? You should know from history that at one time Hindus intermarried with Mughals– who were Muslims. It is also known that Naushervan was married to Maurice, daughter of a Christian King, and her daughter was married to Hindu Chauramni Rana of Udaipur. Daughter of Silyukas, King of Babylon was married to Raja Chandra Gupta. Hirambi, Uloopi and others who were married to prominent men of India were not Hindus. Moreover what is enjoined on the Sikhs with respect to contracting relations with Hindus and individuals of other religions that is stated here:

(ੳ) ਨਾਤਾ ਗੁਰੂ ਕੇ ਸਿਖ ਨਾਲ ਕਰੇ। (ਰਹਿਤਨਾਮਾ ਭਾਈ ਚੌਂਪਾ ਸਿੰਘ)
1. Have relations with a Sikh of the Guru. (Rehatnama Bhai Chaupa Singh)

(ਅ) ਕੰਨਯਾ ਕੋ ਮਾਰੇ, ਮੋਨੇ ਕੋ ਕੰਨਯਾ ਦੇਵੇ, ਸੋ ਤਨਖਾਹੀਆ ਹੈ।
ਸਿੱਖ ਕੋ ਸਿੱਖ ਪੁਤ੍ਰੀ ਦਈ, ਸੁਧਾ ਸੁਧਾ ਮਿਲ ਜਾਇ।
ਦਈ ਭਾਦਣੀ ਕੋ ਸੁਤਾ, ਅਹਿ ਮੁਖ ਅਮੀ ਚੁਆਇ। (ਰਹਿਤਨਾਮਾ ਭਾਈ ਦੇਸਾ ਸਿੰਘ)
2. Killing a daughter or to give a daughter (in marriage) to a non-Sikh, such a person commits great offence. Sikh should give his daughter (in marriage) to a Sikh. Thus Gurmukh meets a Gurmukh. Giving a daughter to a Bhadni (non-Sikh) is like giving nectar to a snake. (Rehatnama Bhai Desa Singh)

(ੲ) ਕੰਨਯਾ ਦੇਵੈ ਸਿਖ ਕੋ, ਲੇਵੈ ਨਹਿ ਕੁਛ ਦਾਮ।
ਸੋਈ ਮੇਰਾ ਸਿਖ ਹੈ, ਪਹੁੰਚੇਗੋ ਮਮ ਧਾਮ। (ਗੁਰ ਪ੍ਰਤਾਪ ਸੂਰਜ)
3. A Sikh gives (in marriage) his daughter to a Sikh and does not accept any money in exchange. He is my Sikh and will reach in my presence. (Guru Pratap Surya)

4. When the daughter comes of age only then relations should be contracted, not for a very young girl. And the relations should be Sikhs of the Guru. (Prem Sumagar)

After Sikh-Hindu marriage why does a Sikh become a Hindu and not the other way around?