Funneling a batch of unrelated old URLs to your homepage doesn’t preserve their traffic, it triggers soft-404 treatment. Google has cautioned that redirecting many or all of a site’s old pages to the homepage is something it reads as soft-404s, which means it largely ignores those redirects and passes none of the old pages’ signals to the homepage. The tidy-looking cleanup keeps nothing and wastes the equity you were trying to save.
The reason is the mismatch. When dozens or hundreds of URLs that each promised something specific all land on a generic homepage, Google compares the destination to what those pages were about, sees that the homepage doesn’t answer any of them, and concludes the redirects are not genuine replacements. So it treats the old URLs as effectively not-found, declines to pass their authority forward, and keeps crawling them as noise while they sit in a soft-404 state, never indexed and never helping.
The fix is to redirect each retired URL to a page that actually relates to it. Where the volume is large, group by section and map in bulk: old blog URLs to the blog index, old product URLs to the matching category, using path-based or pattern rules so it stays manageable. Where a retired page has no relevant home anywhere on the site, let it return a clean 404 instead. Map each URL to a relevant target rather than dumping the whole set on the homepage, and the equity that can move will actually move.