Traditional:

Lime mortars prior to the industrial revolution were very complicated recipes with a half dozen different organic and mineral components carefully selected and prepared using hundreds if not thousands of years of local lore to produce a complicated series of crystal structures that all serve different functions perfectly suited to the local materials and environment. 

Nowadays they consist of industrially produced lime putties or NHL, washed graded sand, plastic fibres and occasionally an industrial by-product made in large industrial mixers. With little thought beyond ease of use and ticking a box marked lime. This description covers the majority of products currently available from lime suppliers.

Putty and sand are far from the most suitable materials for damp or salt rich conditions. And a hot mixed lime mortar with no consideration for aggregates or additives is no better. 

Modern:

Most of these solutions involve one of two things; a barrier to moisture or a cavity of some sort. A barrier destroys the existing masonry and a cavity can trap moisture behind it and hide problems that can cause very serious damage. And both solutions also require such a high standard of work from the installer that is becoming increasingly rarer by the day.

This is covering over the problem and the guarantees for these products cover their individual performance not the solution to the problem. So you could be left with a fully functional system with masonry that has rotten away behind it!

Why not a time proven method that utilises both?

Because Red Mortars have to be made slowly and to order by a Mortarman with more expensive materials which is less profitable than mass producing generic modern building materials in industrial machinery.

The highest performing mortars have to be made on-site with fresh organic materials, locally sourced aggregates/water, expensive lime and require an even higher degree of knowledge and craftsmanship. They often have to be used immediately too as they are usually complicated hot mixed lime mortars. And in a very specific manner otherwise failure can occur. 

However the performance is far superior and time proven in thousands of environments over thousands of years, they’re easier to apply and the aftercare is greatly reduced. So its more economical for the property owner in both initial costs and over a prolonged period compared to the majority of available solutions.

I'm still working on the science but here's a bit;

My red mortar is specified to set at least four times, by chemical, organic and mechanical action. The protein present in the blood that gets separated out by the lime during the slaking process that acts as a natural collagen based proteinaceous glue. It also has a feebly hydraulic set from the 'pozzalonic' materials present followed by carbonation from the lime. The potash contains potassium which contributes to producing ettringite which has two sets as well, initial and then it also autogenously repairs cracks and cavities throughout its lifespan. The potassium present in the potash and blood reacts with the silicate content of the aggregates producing an effect similar to that of a mineral silicate paint, silicification, creating a better bond that reacts with the lime content of both the mortar and the building units producing a far more durable mortar. The ash also contains sulfates which bind with the calcium and produce a small amount of gypsum, which sets faster and stronger than the lime. The oxblood contains phosphate ions which in conjunction with the lime will form carbonated hydroxyapatite crystals. As well as enhancing a lot of other chemical functions. The blood and ash also contain carbonic acid which carbon seeds the mortar. The oil and some of the other materials are utilised to create an effective balance of pores of the correct size range and to provide salt and water resistance primarily through saponification utilising the potassium carbonate from the potash. Which also aids the initial set. The oils must also be precipitated by the use of sea water or another source of salt, usually naturally occuring sources such as potash and blood. The specific order, materials and methodology of mixing are important as something as simple as the blood not being fresh will lessen its effectiveness as would allowing it to cool down too long prior to use. If the lime doesn't reach temperature or if the oil is introduced at the incorrect time it can hinder its functionality rather than improve it too. Using tap water. Not soaking the wood ash. Using iron filings instead of powder. Inaccurate gauging: 1% linseed oil is good, 3% is bad. Raw linseed oil is good but double boiled isn't. Etc, etc...variables. I haven't gone into detail about biomineralisation and promotion of, but suffice to say that is a major factor. 

https://www.youtube.com/watch?v=S1t19oVJhCc&list=PLmJDknXr4_-JbgqQA5-kFdFkD4DL34XM4&index=17

https://www.mdpi.com/2075-5309/12/4/402