That's almost certainly by design. Just as with tweets, it would be massively abused.
It still hasn't been added.
The first x minutes of a post are _heavily_ influential in the success of the post, editing after allows you to hijack successful titles for gain (spam)
For large subs, posts only hit the top of /new for x minutes (for small x), editing after is basically useless if it's not successful in that time
Mods patrol the /new queue as posts come in, allowing editing will complicate moderation which is already a difficult job
Yes it could be misused, but go on any forum where you can edit titles or post content and look at how often such a feature actually does get abused.
It pretty much never happens. Most people (like 99.99% of them) either use the functionality how it was intended or don't bother editing at all.
I don't see the point of limiting a feature because about 0.1% of the userbase might theoretically abuse it in a certain situation. It's basically the social media/forum equivalent of the trolley problem and automated cars. Something that's going to happen very rarely at the most but draws a lot of discussion about 'what ifs'.