Google works just fine.
Spending the money to improve and code a new search function doesn’t gain them anything. They’d just lose money on the implementation.
How do you search by most recent on Google? What does that even mean in the context of searching for web-page content?
Google's search is severely lacking because it's targeting a platform that has no uniform index. This is part of what keeps the public misinformed.
Their presentation would have to model the behavior in a way that feels fresh, but the raw value of their content is already validated. The situation right now is that people’s muscle memory is tied to the verb ‘googling’.
Pushing ‘search.reddit.com’ will not appear different enough to people. They’d have to brand and present it uniquely. It’s a lot more ambitious than pushing their mobile Reddit app, so it’ll never happen.