We are of course aware of this possibility. It would be good for verification, true. But the community has so far chosen not to require it, as it is too easy to forget to enable it, and it would lead to many rejected otherwise good submissions. Especially since the enable replay button defaults to "off", and it reset to "off" by Factorio even if you previously enabled it (Unless you use the secret setting in "the rest" hidden settings, but too many people do not know that).
Adding additional requirements to submissions is a balancing act between verification and user friendliness. I think the reasoning for not requiring replay is that cheating is probably not a big enough problem in this community to add cumbersome requirements. The community runs on trust.
The requirements for submissions are subject to change, and are voted on by people who have submitted speedruns to the leaderboard, via the discord.
The notifications i get for Factorio are falsely claiming that literally every new run is a new WR, which is obviously untrue.
For example the top run in the screenshot is not a real WR, see the category: https://www.speedrun.com/factorio?h=Any_MP&x=wkpjq9wk
People tend to overlook stuff like that, if it is only in the rules (the rules do already specify "permanent video"). So having it in the rules would not alleviate the need for an admin to manually check all new submissions.
Surely this is not just a problem for Factorio, but for basically all speedrun games. Which is why I am suggesting as a general site feature.
I am part of the Factorio Speedrunning community. A problem we have is that people are submitting runs with video links linking to twitch VODs which are not highlights. Then eventually Twitch auto-deletes them, and history is lost.
It would be very useful if speedrun.com supported a setting to auto-reject non-highlight Twitch video links.
There is a Twitch API which can be used to determine if a video is a highlight or not: https://dev.twitch.tv/docs/api/reference#get-videos