That is bad if true but if the alternative is for those investors to buy some other units elsewhere it's still useful to build this to prevent them from doing that.
Foreign investors seem to be biased towards new-build property, I'm not sure why. "Elsewhere" could easily mean an entirely different country.
Units in SF built after 1979 are not subject to rent control.
New builds involve dozens of units coming to market at once. Thus, sales and marketing teams can be employed to market the property overseas to these wealthy individuals. It's also far more predictable and doesn't require inspection and such. In some markets, such as Australia (possibly UK, I'm not sure), you don't pay property tax but you do have an upfront stamp duty. This duty is waived for purchases of new developments (another way foreign investors get to pilfer commonwealth countries and take advantage of so many of the benefits of living there without paying much tax at all).