Some possible reasons:

 

-- RLP systems are only advantageous for guns that use separate projectile and incremented propellant charges.  For NATO this would mostly be the 155mm systems. 

-- RLP is probably only usable on self propelled guns due to added weight, complexity, and power requirements.

-- None of the advantages you listed, either singularly or together, provides a 'show stopping' advantage.  And, unlike other changes in gun systems, RLP represents a significant change in the weapon itself, rather than an incremental improvement.  Hence it has the potential for actual failure, rather than just not living up to it's hype.  That can terrify a bureaucrat into indecision.

-- Reliability.  You are injecting a large amount of propellant very quickly into the combustion chamber at extremely high pressures while the gun is firing.  Nobody has any idea how it will stand up in actual use with field maintenance.

 

-- Competition.  RLP systems are only one of many concepts that are competing with each other for the next big thing in guns, including rail guns, electrothermal propulsion, various plasma enhanced combustion concepts, new propellants, and dual charge propulsion.  Currently no one design has a clear advantage over the others when all factors are taken into account.

Liquid propellant has seemed like an obvious good idea for the last 50 years or more, and has been proclaimed as coming real soon on several occasions.  The attraction is less propellant to carry around.  Originally Crusader was gpoing to use, in the event it was dropped during development IIRC.

 

One scientist working in the field said the problem in one word to me "oxidiser".

My layman's first thought is " What if it leaks?".. 

Until the rail-gun arrives (with its own problems), some of the major advantages of the RLPG would however seem to be substantial:  instant infinitely adjustable charge and easier transfer of propellant - just pump it.

 

 

 

The gun crew dies.

Are the chemicals which would be used in such a Liquid Propellant really that nasty?  As mentioned by Neutraliser UDLP initially envisioned the XM2001 Crusader as being a liquid propellant gun but after the third instance of "Energentic Venting" and "High Speed Dissassembly" on the ordnance test bed that approach was abandoned!!!!!

There isn't a hypergolic of which I know that isn't deadly in some "interesting" way. Not to mention, that pressure overburden is the classic way we produce fragmentation effects.

 

 

 

the propellant HAVE to be hypergolic?  Just asking...A fuel and an oxidizer, yes, but why not an external igniter, be it a hot wire, or a primer like artillery currently uses?

 

Liquid propellant has been a mil Sci-Fi staple for decades...and every year is "Next Year Jerusalem."