Because if you take the trouble to write that out, there will still be slightly more pressure on the receiver to reciprocate by giving a more formal reply, despite the surface content.
I think "how hard is it?" is the wrong question. We should be asking "how can this be better?". It doesn't take very long to type something like "as far as I know", but we still routinely use acronyms like AFAIK, because as long as everyone knows what it means, it's often a waste of time to type the full thing out. The only difference here is that VSRE is not already a custom.
AFAIK, IMHO, INAL, etc. work because they are acronyms for very common phrases. Intelligent people can reason out their meaning based on context without you having to spell them out. That's why they are popular and why they work. There was never a global memo "Hey everybody we're going to start using AFAIK now."
VSRE doesn't work. It's better to just type out what you want to say in this case.
You just say "VSRE doesn't work" without mentioning that the only reason is that people don't already say it. That's my point. Maybe we can agree that we shouldn't jump straight to the acronym. But if we want this kind of custom, and I do, it has to start somewhere, not with a global memo but with people just doing it. I'm just going to start saying "short reply ok". With any luck that will catch on, and then we can abbreviate to "SRO" or whatever people wind up using, and the world will be an ever so slightly more efficient place.
I think "how hard is it?" is the wrong question. We should be asking "how can this be better?". It doesn't take very long to type something like "as far as I know", but we still routinely use acronyms like AFAIK, because as long as everyone knows what it means, it's often a waste of time to type the full thing out. The only difference here is that VSRE is not already a custom.