1. For the same reason as solving sudoku online i.e. for the joy of it.
2. Some interesting literature was written in Sanskrit. I may want to read that.
3. To be able to judge when a hindu preacher is bullshitting me.
4. To be able to critically analyze some of the religious stuff e.g. does the age of Sun god tally with what the modern physics tells us.
5. Its grammar expands my view of what is possible to express in a language.
6. For the same reason as pursuing archaeology. The words in a dead language can tell you a lot about the life when it was in common use.
I see that you substantiate some of your views with a "P.S." that you were forced to learn it for 3 years. That means nothing. I learnt it for 5 years purely to pass exams but that hardly makes me qualified enough to start judging whether others should learn it or not.
Nopes I don't know Sanskrit and it is not on my radar right now. But a while ago when I tried to learn German, faint memories from Sanskrit classes came quite handy(see #5 above).