I can't see a direct relation between these. Cash transactions are convenient enough to me.
Yeah cash transactions are convenient. So why would someone go for bitcoin? Where small transactions can take quite long to get verified (ignoring the lightning network implementation). And can the convenience factor of UPI hinder in bitcoin adoption?
Does the number of people matter? Would you argue in favor of UPI because most of the people would not care?
No. But won't adoption matter in terms of trust in bitcoin, and how stable it is at any point?