I think the reason why people assume your not spiritual if you don’t attend sem is because it so common to go. In other words, being that it is so accepted to go to seminary, it’s just one more year of learning and growing – people jump to conclusions that obviously you’re not interested in growing. Because why else would you give up a year most girls look forward to?
As for why people make it into something you have to do, I’m unsure. But society dictates. It’s your choice whether you want to follow or not.