S&W has kept the lid on walther for many years... If you were the importer for a competitors product, would you really talk it up an take away from your sales?
While that's an interesting theory and arguably true today, I don't think it was true even 5 years ago. Prior to the release of the M&P line, S&W had very little to lose in promoting Walther products because they offered few products that directly competed with anything Walther made. Lack of promotion for the P99 made sense because S&W was successfully chasing American LE contracts with the license-built SW99 and Walther was getting a slice of the pie.
Even today, I think that S&W loses nothing by promoting the PPK line, since the company arguably doesn't offer anything that directly competes with it; the BG380 is quite different and IMHO appeals to a lower-end market segment.
I'd argue that another factor leading to this situation was Walther's historically conservative marketing philosophy. When it comes to full-size combat pistols, for many decades, Walther seemed to believe that European LE/military contracts were their meat and potatoes and that the American commercial market was just icing. The commercial P1/P38, P5, and P88 had very little American market presence. It's quite possible that the success of HK, SIG Sauer, and (most notably) Glock at playing both
markets has caused Walther's management to change its philosophy.