Ahead of the Asian Economic Community in 2015, there are a number of basic infrastructure projects that need to be completed, among them ae road/rail/port upgrades.  the region is growing rich enough that it is not nearly as dependent on investment from the first world of the West as it was previously.  Vietnam is investing heavily in Cambodia, for instance.  Here is another example of that. 

Malaysia using its relatively vast pool of capital to invest in Myanmar is an important step in promoting not only growth for growth's sake but for creating a tighter knit ASEAN as things progress.  China's influence in both Cambodia nad Myanmar is extensive and the issues surrounding the South China Sea are creating rifts within ASEAN.

I would be shocked if it wasn't Petronas, Malaysia's Oil and Gas giant, that is looking to expand their investment next door, seeing as their needs for energy are becoming acute.