This was (and is) a one-way trend for document corroboration. Before 1987 a taxpayer could pretty well claim any itemized deductions with no documents required.
Even before then, the "TEFRA" act (1982) began the issuance of 1099s to recipients for services rendered. Nowadays look at the itemized deductions. Mortgage interest deductions are supported by 1098s, education credits supported by 1098-T, student interest supported by 1098-E, etc. Not to mention the standard deductions are so large most people cannot itemize anyway.
Also, in earlier days, tax rates were higher, such that tighter control of expenses could justify lower rates (which were broadly announced to delight the public)
And we also have the thinly disguised effort to make auditors of taxpayers via the 8867. Although the IRS denies it - the mechanics of correctly navigating through the 8867 really means much of the busiwork of an audit has been transferred to the preparer. Self-prepared returns don't require an 8867.
And the legislation making its way through congress does nothing to reverse the trends.