I suspect two things to be at work here (among possibly many):
- First, reciprocity. If you send me an email with a one-liner, I will feel that replying in kind would be adequate. A verbose email on the other hand, may have the opposite effect of creating a feeling that I should also be more detailed (which you may not even need). My response might be to set your email aside with the purpose of addressing it later when I have more time (we all know that famously elusive promise of a future that never materializes).
- The second point is slightly in line with the previous, but different. The length of the message can be used to estimate the cost of a conversation. A short message can be perceived to announce a one-off (cheap) exchange, whereas a verbose message may seem like the beginning of a more involved (expensive) one where if I engage, you will ask even more from me (how much exactly, nobody knows). That uncertainty is uncomfortable enough that I may not want to respond at all.
- First, reciprocity. If you send me an email with a one-liner, I will feel that replying in kind would be adequate. A verbose email on the other hand, may have the opposite effect of creating a feeling that I should also be more detailed (which you may not even need). My response might be to set your email aside with the purpose of addressing it later when I have more time (we all know that famously elusive promise of a future that never materializes).
- The second point is slightly in line with the previous, but different. The length of the message can be used to estimate the cost of a conversation. A short message can be perceived to announce a one-off (cheap) exchange, whereas a verbose message may seem like the beginning of a more involved (expensive) one where if I engage, you will ask even more from me (how much exactly, nobody knows). That uncertainty is uncomfortable enough that I may not want to respond at all.