Going back to the original thread starter question, there is a reasonably accurate history of MLS development here:
https://en.wikipedia.org/wiki/Microwave_landing_system
At a meeting of the Royal Institute of Navigation at Canary Wharf London in 1994, the USA presented a number of papers defining the GPS system.
Many Europeans present were outraged that the USA had developed this system without their participation or consultation. Seriously, it's true - I was there. The USA members were somewhat taken aback, this was their system designed for their military but with free access available to the Standard Positioning System to any and all users.
Then and there, the European members resolved they were going to have their own Sat Nav system because they did not trust the USA and its total control of GPS. That was the intellectual birth of Galileo back in 1994. How is that going, fully operational yet?
At that time MLS was officially approved by ICAO and was to become mandatory fitment in the future, BUT
ICAO held a special COM-OPS division meeting in Montreal in 1995.
The Australian company I worked for held a reception for all delegates promoting our AWA-Intescan MLS ground equipment.
The next day and at that meeting, the USA delegate read out a letter from President Clinton offering ICAO free use of GPS into the future and guaranteeing at least seven years notice of withdrawal. He also indicated that the "dithering" or positional degradation then operating on the Standard Positional Service (Accuracy CEP of 100 feet) would be turned off thus improving accuracy of SPS by an order of magnitude.
That meeting was the end of the road for MLS as an ICAO mandatory fitment item. And FREE beats COSTLY every time. Precious few operators or authorities were prepared to continue with an MLS program in these circumstances.
Certainly some countries in Europe continued with MLS installation for various local reasons including frequency congestion, interference with ILS, and plain distrust of GPS. A couple of military MLS systems also were installed in Asian countries but general development of the system virtually ceased.
GPS WAAS and its variants plus GBAS systems (Ground Local Area Augmentation Systems) are becoming the future and there are GBAS systems in Air Transport use in various parts of the world.
Hope that answers the original question!