Are you counting Catholics among those Christians for whom attendance is “mandatory”?
I do know that in some of the more “mainline” historical Protestant denominations, regular weekly church attendance is very, very low, and while it might be seen as unfortunate, for a member to show up only at Christmas and Easter, or even sporadically throughout the year, there is no thought of their having sinned by not showing up every week.
While there is a canonical Sunday/HDO Mass obligation (a most unfortunate word), there are many common-sense exceptions, such as being sick or contagious, having family members who need care, being forced to work by one’s employer, being a great distance from any church, and so on. Good rule of thumb, if you are too sick to go to work or to school, you’re too sick to go to Mass.