While I cannot be sure of the drop in the number of tax return preparers that has been reported being accurate I can see that with the changes in the tax laws since 2017 that has happen there would be a drop in the number of tax return preparers that would be needed. With the elimination of so many tax reductions and the increase of the standard deduction  schedule a has in many cases become something of the past.  And if the income being reported is strictly from wages , interest and dividends. and retirement income why would anyone with an 8th grade education need an outside tax preparer.