Reasons medics don't revive you: -
They do not see your corpse behind them
They may well be 1 meter away, but they are very likely looking a different way.
There should be a distance indicator showing corpses to medics, like there is for showing medics to corpses, imho
Your corpse is rarely where you think it is
You more often than not fall/slide/move after you die. Your killcam and the medic distance indicator is relative to the wrong place. The medic that is "right on top of you" probably is not and probably cannot see you at all.
Your corpse might be in a very dangerous place
Your killcam isn't 360 degrees and they may very well not be able to get to you safely and you wouldn't know.
You're not a nice person
Maybe one of the above happened and you moaned about it. It always amazes me when people do this. Do you think abusing the people you want something from is a good idea?
They don't have a syringe
I know medics that run with both pouches and crate. There's various reasons, but mostly they get fed up with people skipping when safe or not skipping when in danger.
I also know medics that run with pouches/crate and rifle grenade. It's a medic gadget. There are even medals requiring it. Grow up and get over it.
Medicking is possibly the toughest thing to do in BF1. People do not pick medic to get great KDs and to please themselves. Yes, you can heal yourself, but the SLRs are more than enough of a balance - BF1 medics are not like BF4 assault class. Give them a break.