This is what you call a quick fix . the USA market went about requesting a manual transmission for the M5 BMW simply utilised the transmission which was already available for the 5er . BMW are not offering the transmission in europe because the marketing in europe is connected to BMW's F1 business with regards to the SMG III transmission - So by bringing out a manual could almost make SMG III and BMW's marketing redundant . And of course there has been no major demand for a manual gearbox in Europe - Besides the SMG III is quite an achievement.
The M3 will be offered with SMG and another transmission currently in development.