Well, firstly, there’s the fact that the HA was a volunteer organization that supposedly only got by through donations, though we know they’ve been making money through exploiting monsters like that one pangolin monster that generated a kind of material they could sell for a lot of money.
Secondly, the S Class appeared within the first few months, giving the public their first taste of just what “the strongest” looked like. The fact that they joined the HA in the first place was quite the lucky coincidence, since we’ve seen other similarly skilled reluctant to join and associate themselves with the hero profession.
Which leads to the next point; things have rapidly gone hot in the recent months since the story began, with more frequent appearances of higher disaster level threats. Before this point, there was no major dissatisfaction with the HA. It’s only with these frequent occurrences that the HA’s ability to deal with all threats quickly and safely (safety in that the heroes dispatched are safe and sound, inspiring confidence in the civilians) has been called into question. Hence what BS said about the MA’s attack not being for nothing.