Are layoffs like a fashion statement, now? "Look, we're cool, too!" why is everyone doing this at the same time?
And same percentages! https://www.marketwatch.com/story/pagerduty-to-lay-off-7-of-... https://www.calcalistech.com/ctechnews/article/hjyj6811as https://www.theglobeandmail.com/business/article-hootsuite-r... https://variety.com/2023/digital/news/vox-media-layoffs-130-... etc....
So if the layoffs come not because of hard "we have x to much cost" reasons but of "we need to be more robust for potential dives in profit and increased cost" reasons and an arbitrary number must be chosen which isn't affecting operation too much but also makes a difference 7% is a common choice "because that worked well for some other large companies". Especially when the push comes from shareholders without much company insight 7% is likely.
If your company is smaller you make decisions on a one by one basis (after having some target for rough performance where you cut). But the moment your company has 100+ or even 1000+ people that gets impractical so a % line is set for how many people need to be cut.