A few possible reasons but nothing that wouldn't apply to any other nationalities/races learning any other language. Wonder why you mentioned Indian people and Spanish in particular? I noticed you are also learning Hindi, so likely for much the same reasons. I think Spanish as a language sounds great when spoken and sung and it is useful to know when visiting South America, Spain and even the US has a sizeable population of Spanish speakers.
- like the culture
- like the songs
- have a relative(s) who speaks Spanish
- wants to travel to Spanish speaking countries or work there
- has many Spanish friends or would like to make Spanish friends
- interested in language learning itself
- a current job requirement / posting
- doing research
- has a Spanish girl/boy friend or wife/husband (or would like one)
- has some Spanish heritage
- likes Spanish food
- bored
- likes the sound of the language
- mind training
- to enhance their travel experiences