A company has to defend its trademarks in order for something like that to be upheld. The problem is that there are already hundreds of software companies with "soft" suffixed names. Because Microsoft was likely not the first software company to use the "soft" suffix, nor have they taken action to shut down any of these other companies, they can't suddenly do an about-face and claim trademark dilution against one of them (maybe unless there was more to it than a -soft name, e.g. a logo closely resembling Microsoft's, or other attempts to trade on Microsoft's reputation).