In terms of statistics, a 2010 study shows that seven out of ten people do not file their own tax returns. This demonstrates that preparing an ordinary personal tax return has become very complicated.
There are various kinds of credits, like the one given for public transit passes, that are given in communities like mine where there is no bus. These credits only weigh down the legislation and make it harder to know how much it costs compared to what the taxpayer must pay in compliance costs. But I don't have the numbers.
It is only logical that any time a tax form is made more complicated, it becomes harder and harder for people to prepare their own tax returns. So people are spending their money on accounting fees. Our profession is probably the only one that is in no danger of disappearing.