From what I've been told, the company wants to be able to market a standard size plastic pistol that can be sold as low as down in the $250 range, for buyers interested in a low cost, affordable, decently made handgun for home/self defense.
I once asked if there was going to be an armorer class for the SD. The answer was no, and the reason offered was that the SD line wasn't intended for LE sales, so there was no anticipated need for LE armorer training for the SD line.
I can't remember the last time I saw the older Sigma line included in the list of armorer classes, but it's been a while. My class was toward the end of the 90's, and there were revisions occurring after that time.
I've never even looked inside the SD series, nor fired one.
The armorer class for the SW99/P99 pistol was dropped from the list of available armorer classes, too, although I was told that the S&W academy would still provide armorer recert for an existing agency customer if they continued to use the SW99's (if they hadn't been able to be talked into trading them for M&P's). I was told of one such special agency, off the public radar, so to speak, who had (then) recently requested such a class for their SW99's.
I was surprised any of them were still in-service. I can't imagine the SW99's (or 990L's) would remain in-service as agency weapons for too many more years, not only because the model line was discontinued, but because S&W was apparently no longer going to be ordering repair parts from Germany, and had reportedly (what I was told) sold off most of their existing parts to the new Walther importer when they closed down their Walther America business.
EDITED to add: Don't mistake my above comment about being surprised any were still in-service as being in any way an inference that the quality of the S&W licensed version of the Walther P99 series is inferior or substandard. Quite the contrary. I've long believed the 99 series, and especially the SW99's, were excellent, robust and reliable duty/defensive-type pistols. I own a pair of them, carried an issued one for a few years (and used it for training/drills & quals, firing several thousand rounds), and have fired many more rounds through other examples of them. I like them, with the minor exception of the early backstrap inserts being less-than-optimally ergonomic. To be fair, though, Walther did pretty much invent the idea, and has revised them over time.
I ordered enough spare/repair 99 parts, as an armorer, to enable me to my own SW99's up and running for probably the rest of my life (and those of a couple of friends).
I imagine at some point I'll have to start ordering replacement RSA's and mag springs from the new Walther importer, though.
I believe S&W's target market is mainly home and personal defense, and for that it is adequate if it's all you can afford.
