Hello Kevin,
Interesting research. I would just like to make a few comments:
Isnt it a tragic that a sport hundreds of years old( as is Muay Tha)i is dependant upon a sport 20 years old( MMA) to have its right to exist?
Before internet coverage at least KI kick-boxing was very popular in Europe because of Eurosport on cable TV. Also shown were Muay-Thai bouts from a TV studio in Bangkok. What ruined the Muay-Thai reputation were the first UFC events which showed that BJJ was superior to MuayThai, or in more general terms- grappling was superior to striking. Lately this has been partially refuted by the rise of Jose Aldo, Cowboy Cerrone, and Joanna Jedrzejczyk,.but in general to succeed in MMA you need a solid BJJ and wrestling base.
When K1 went bankrupt in 2010 alot of careers were cut short. Here is a great documentary about the rise and fall of kickboxing: http://www.damientrainor.com/2014/shin-on-shin-kickboxing-documentary-series
I think one reason Muay Thai never caught on in USA were the leg kicks, the clinch, and elbows. The elbows were a source of contention for years in Germany. The MTBD( formed in 1984) wouldnt allow elbows for years in competition because of the danger of cuts and bad concussions. The Americans had their PKA Karate going, and low kicks were considered the height of dirty fighting!!
Now in 2015, because of years of MMA (Formerly known as fighting without rules) exposure, the threshold for violence has fallen so much, that bloody cut up faces and brutal KOs, and broken arms mean nothing anymore and are considered normal.
I would guess that the rise of interest in Italy for Muay Thai is due to Stefanie Picelli and her Yokkao branding which includes her promotions, fight gear and her seminars with Senchai and Pakorn.
In Brazil I would guess it is the popularity of Anderson Silva and Jose Aldo that spark interest in Muay Thai in the land of the Jui-Jitsu masters.
My theory for the stagnation of Muay-Thai would include career possibilities as a hindrance to growth. As Sylvie has pointed out most Thai women give up fighting in their 20s because their is no path to abundance. For the men in Thailand it is probably not much better.
In the West because of the dominance of MMA the only way that promises financial reward is UFC, Bellator, and for women Invicta. For MuayThai you have Lion Fight or Glory for Kickboxing which I am sure, do not pay well since they are small organizations still establishing themselves.
Another problem with the olympic acceptance of Muay-Thai is the inability to organize all the South East Asian fighting styles under one banner. Burma has Lethwei, Cambodia has Pradal Serey, Laos has Muay Lao, and Malaysia has Tomoi etc. These fighting styles are all similiar and sometimes indistinguishable from Muay-Thai but are not recognized as such by Thailand, or the international community due to politics and nationalism.
The key to more growth for Muay-Thai world wide is "More Money" for fighters, more televised shows in the West, a magazine comparable to the high gloss "Fighters Only" for the MuayThai community and olympic recognition.