Whereas the vast majority of astrophysicists support the big bang theory, many nonscientists consider the theory to be controversial. why do you think so many people might object to the theory?

Undoubtedly because they lack the education, experience, subject knowledge, or raw brain cells to comprehend the evidence on which the theory rests.  OR they just haven't taken the time to READ the evidence yet.

It's the same thing that you find in the areas of the shape of the Earth, or the existence and causes of climate change.  It's always the people with the least to say who are doing the most, loudest talking.

Here's an example:  I'm writing this in early June, 2019.  There's a group of these people who, when Climate Change comes up for discussion and action,  beg themselves out of the discussion, saying "I'm not a scientist.".  But only a short time later, when it comes to debate and legislation on abortion rights, those are the SAME people who suddenly claim to possess the knowledge and informed judgement of competent gynecologists.