At the start of the year, the OPM announced that federal workers could either take a voluntary resignation and go on paid leave until Sept. 30 (today), or be subject to return-to-office orders (including forced relocation if necessary), higher performance standards, and further involuntary layoffs. According to this article, about 100,000 people took the voluntary resignation.
As for motive, it's a way for the Trump admin to clear out the federal workforce and install loyalists to make it easier for him to carry out his agenda.