I am not yet knowledgeable enough about the Sikh faith to comment on why your specific faith isn't more numerous. But Bahais face the same problem about 7 million world wide. If Baha'ism is the new revelation for our time, it hasn't seem to caught on!!
I spent most of my life seeking a deeper path of faith. What I've found is that there are lots of religious people. Yet, with so many it is only surface deep. There are many who just uncritically accept the faith of their parents and community. Many are unaware, in any real way, of faiths outside their own. True, deep mystical faith is rare.
I spoke with this about a Rabbi once and I talked to him about seeking God's Holiness. I said well doesn't everyone? What I meant isn't everyone trying to be a good person, don't most people believe in some higher power. The Rabbi said "No, most people don't seek it". I think the Rabbi's right. Not many give up everything to seek God.
So census numbers doesn't prove one's truth of revelation. God is present to all of us, I think. Yet, only a few are called deeper to Him. It's a mystery. Living in a Bible belt town in the American south, I'm one of the few mystics I know. Praying multiple times a day and studying scripturers for myself is rare. We shouldn't compare ourselves to the majority.
I don't know if that was reassuring or not. We seek to serve and love God. I don't care about our census results!