Figures published on Thursday following an investigation by The Scotsman and other media outlets show only 5 per cent of all complaints were subject to a full investigation.
In total, 122 of the 2,613 complaints made about care homes for older people were investigated fully by the Care Inspectorate a drop from around 600 in previous years.
The Care Inspectorate defended the drop in full investigations, saying the move away from in-person inspections was required as the risk of Covid-19 transmission grew.
The body said it increased the use of technology and contact with care providers during the pandemic to combat the change of approach.
The Scottish Government said it had committed to a public inquiry into the handling of Covid-19 and a review of social care that will likely lead to the creation of an as-yet undefined National Care Service.
Scottish Liberal Democrat leadership hopeful Alex Cole-Hamilton said there was “no excuse” for not fully investigating complaints, while the Scottish Greens said the drop was “inexplicable”.
The Scottish Conservatives’ health spokesperson, Annie Wells, said scrutiny had “taken a back seat”.
She said: “Care home residents and their families have suffered so much since the start of the pandemic. Their needs were completely forgotten about by the SNP.
"That led to the scandal of untested patients being sent to homes straight from hospital, with tragic consequences and when they most needed advocates, scrutiny has taken a back seat.
"There is only so much that can be done remotely and an online meeting is no substitute for in-depth inspections.
"The long-awaited public inquiry into the SNP Government's handling of Covid will contain volumes on what went wrong in care homes. Families are waiting for answers."
Mr Cole-Hamilton, the Liberal Democrat’s health spokesperson, said the rights of care home residents were “sadly neglected”.
He said: “The workload of the Care Inspectorate is obviously considerable, but that's no excuse for not affording these issues a proper investigation.
"The dispatch of Covid-positive and untested patients into Scottish care homes was an error of the gravest nature. Today's revelations show one again that the rights of care home residents have been sadly neglected."
Gillian Mackay, the Scottish Greens’ health spokesperson, said the drop in complaint investigations was “inexplicable” and that she would raise the issue with ministers “immediately”.
She said: “The sheer scale of care home deaths, particularly at the beginning of the pandemic, is staggering.
“The failure of the Care Inspectorate to investigate such a substantial number of complaints, at a time when we were seeing unprecedented loss of life in care homes, is inexplicable.
“While I’m sure that the public inquiry into the handling of coronavirus will look into this as part of its work, I plan to raise these serious matters with ministers immediately. There is no need to wait for that inquiry before seeking answers to important questions about the regulation of the care sector.”